Index: doc/next-migration.html =================================================================== diff -u -rf934951db464db1a6f39ac98290ecde17a466cd7 -rc4f449cb353be812ba6502ef8e9587e87881f59b --- doc/next-migration.html (.../next-migration.html) (revision f934951db464db1a6f39ac98290ecde17a466cd7) +++ doc/next-migration.html (.../next-migration.html) (revision c4f449cb353be812ba6502ef8e9587e87881f59b) @@ -1,6473 +1,6473 @@ - - - - - -Migration Guide for the Next Scripting Language - - - - - + +
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+
+
+
+
Abstract
+

This document describes the differences between the Next Scripting +Language Framework and XOTcl 1. In particular, it presents a +migration guide from XOTcl 1 to NX, and presents potential +incompatibilities between XOTcl 1 and XOTcl 2.

+
+

The Next Scripting Language (NX) is a successor of XOTcl 1 and is +based on 10 years of experience with XOTcl in projects containing +several hundert thousand lines of code. While XOTcl was the first +language designed to provide language support for design patterns, the +focus of the Next Scripting Framework and NX are on combining this +with Language Oriented Programming. In many respects, NX was designed +to ease the learning of the language by novices (by using a more +mainstream terminology, higher orthogonality of the methods, less +predefined methods), to improve maintainability (remove sources of +common errors) and to encourage developer to write better structured +programs (to provide interfaces) especially for large projects, where +many developers are involved.

+

The Next Scripting Language is based on the Next Scripting Framework +which was developed based on the notion of language oriented +programming. The Next Scripting Frameworks provides C-level support +for defining and hosting multiple object systems in a single Tcl +interpreter. The whole definition of NX is fully scripted +(e.g. defined in nx.tcl). The Next Scripting Framework is shipped +with three language definitions, containing NX and XOTcl 2. Most of +the existing XOTcl 1 programs can be used without modification in the +Next Scripting Framework by using XOTcl 2. The Next Scripting +Framework requires Tcl 8.5 or newer.

+

Although NX is fully scripted (as well as XOTcl 2), our benchmarks +show that scripts based on NX are often 2 or 4 times faster than the +counterparts in XOTcl 1. But speed was not the primary focus on the +Next Scripting Environment: The goal was primarily to find ways to +repackage the power of XOTcl in an easy to learn environment, highly +orthogonal environment, which is better suited for large projects, +trying to reduce maintenance costs.

+

We expect that many user will find it attractive to upgrade +from XOTcl 1 to XOTcl 2, and some other users will upgrade to NX. +This document focuses mainly on the differences between XOTcl 1 and +NX, but addresses as well potential incompatibilities between XOTcl 1 +and XOTcl 2. For an introduction to NX, please consult the NX tutorial.

+
+
+
+

1. Differences Between XOTcl and NX

+
+

The Next Scripting Framework supports Language Oriented Programming +by providing means to define potentially multiple object systems with +different naming and functionality in a single interpreter. This +makes the Next Scripting Framework a powerful instrument for defining +multiple languages such as e.g. domain specific languages. This focus +differs from XOTcl 1.

+

Technically, the language framework approach means that the languages +implemented by the Next Scripting Framework (most prominently XOTcl 2 +and NX) are typically fully scripted and can be loaded via the usual +Tcl package require mechanism.

+

Some of the new features below are provided by the Next Scripting +Framework, some are implemented via the script files for XOTcl 2 and +NX.

+
+

1.1. Features of NX

+

In general, the Next Scripting Language (NX) differs from XOTcl +in the following respects:

+
    +
  1. +

    +Stronger Encapsulation: The Next Scripting Language favors + a stronger form of encapsulation than XOTcl. Calling the own + methods or accessing the own instance variables is typographically + easier and computationally faster than these operations on other + objects. This behavior is achieved via resolvers, which make some + methods necessary in XOTcl 1 obsolete in NX (especially for importing + instance variables). The encapsulation of NX is stronger than in + XOTcl but still weak compared to languages like C++; a developer can + still access other objects' variables via some idioms, but NX makes + accesses to other objects' variables explicit. The requiredness to + make these accesses explicit should encourage developer to implement + well defined interfaces to provide access to instance variables. +

    +
    2. +
  2. +

    +Additional Forms of Method Definition and Reuse: + The Next Scripting Language + provides much more orthogonal means to define, reuse and + introspect scripted and C-implemented methods. +

    +
      +
    1. +

      +It is possible to use NX alias to register methods + under arbitrary names for arbitrary objects or classes. +

      +
      2. +
    2. +

      +NX provides means for method protection (method modifiers + public, protected, and private). Therefore developers have + to define explicitly public interfaces in order to use methods + from other objects. +

      +
      3. +
    3. +

      +One can invoke in NX fully qualified methods to invoke + methods outside the precedence path. +

      +
      4. +
    4. +

      +One can define in NX hierarchical method names (similar to + commands and subcommands, called method ensembles) in a + convenient way to provide extensible, hierarchical naming of + methods. +

      +
      5. +
    5. +

      +One can use in NX the same interface to query (introspect) + C-implemented and scripted methods/commands. +

      +
      6. +
    +
    3. +
  3. +

    +Orthogonal Parameterization: + The Next Scripting Language provides an orthogonal framework for + parametrization of methods and objects. +

    +
      +
    1. +

      +In NX, the same argument parser is used for +

      +
        +
      • +

        +Scripted Methods +

        +
        • +
      • +

        +C-implemented methods and Tcl commands +

        +
        • +
      • +

        +Object Parametrization +

        +
        • +
      +
      2. +
    2. +

      +While XOTcl 1 provided only value-checkers for non-positional + arguments for methods, the Next Scripting Framework provides + the same value checkers for positional and non-positional + arguments of methods, as well as for positional and + non-positional configure parameters (-parameter in + XOTcl 1). +

      +
      3. +
    3. +

      +While XOTcl 1 supported only non-positional arguments at the + begin of the argument list, these can be used now at arbitrary + positions. +

      +
      4. +
    +
    4. +
  4. +

    +Value Checking: +

    +
      +
    1. +

      +The Next Scripting Language supports checking of the input + parmeters and the return values of scripted and C-implemented + methods and commands. +

      +
      2. +
    2. +

      +NX provides a set of predefined checkers (like e.g. integer, + boolean, object, …) which can be extended by the + applications. +

      +
      3. +
    3. +

      +Value Checking can be used for single and multi-valued + parameters. One can e.g. define a list of integers + with at least one entry by the parameter specification + integer,1..n. +

      +
      4. +
    4. +

      +Value Checking can be turned on/off globally or on the + method/command level. +

      +
      5. +
    +
    5. +
  5. +

    +Scripted Init Blocks: The Next Scripting Language provides + scripted init blocks for objects and classes (replacement for the + dangerous dash "-" mechanism in XOTcl that allows to set variables + and invoke methods upon object creation). +

    +
    6. +
  6. +

    +More Conventional Naming for Predefined Methods: The naming of + the methods in the Next Scripting Language is much more in line with + the mainstream naming conventions in OO languages. While for example + XOTcl uses proc and instproc for object specific and inheritable + methods, NX uses simply method. +

    +
    7. +
  7. +

    +Profiling Support: The Next Scripting Language provides now two + forms of profiling +

    +
      +
    • +

      +Profiling via a DTrace provider (examples are e.g. in the dtrace + subdirectory of the source tree) +

      +
      • +
    • +

      +Significantly improved built-in profiling (results can be + processed in Tcl). +

      +
      • +
    +
    8. +
  8. +

    +Significantly Improved Test Suite: The regression test suite of + Next Scripting Scripting framework contain now more than + 5.000 tests, and order of magnitude more than in XOTcl 1.6 +

    +
    9. +
  9. +

    +Much Smaller Interface: The Next Scripting Language has a much + smaller interface (i.e. provides less predefined methods) than + XOTcl (see Table 1), although the expressiveness was increased in + NX. +

    +
    10. +
+
+ + ++++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
Table 1. Comparison of the Number of Predefined Methods in NX and XOTcl
NXXOTcl

Total

45

124

Methods for Objects

14

51

Methods for Classes

9

24

Info-methods for Objects

11

25

Info-methods for Classes

11

24

+
+

This comparison list compares mostly XOTcl 1 with NX, some features +are also available in XOTcl 2 (2a, 2c 2d, 3, 4).

+
+
+

1.2. NX and XOTcl Scripts

+

Below is a small, introductory example showing an implementation of a +class Stack in NX and XOTcl. The purpose of this first example is +just a quick overview. We will go into much more detailed comparison +in the next sections.

+

NX supports a block syntax, where the methods are defined during the +creation of the class. The XOTcl syntax is slightly more redundant, +since every definition of a method is a single toplevel command +starting with the class name (also NX supports the style used in +XOTcl). In NX, all methods are per default protected (XOTcl does not +support protection). In NX methods are defined in the definition of +the class via :method or :public method. In XOTcl methods are +defined via the instproc method.

+

Another difference is the notation to refer to instance variables. In +NX, instance variable are named with a single colon in the front. In +XOTcl, instance variables are imported using instvar.

+
+ +++ + + + + + + + + + + + +
Stack example in NX Stack example in XOTcl
+
+
Class create Stack {
+
+   #
+   # Stack of Things
+   #
+
+   :variable things ""
+
+   :public method push {thing} {
+      set :things [linsert ${:things} 0 $thing]
+      return $thing
+   }
+
+   :public method pop {} {
+      set top [lindex ${:things} 0]
+      set :things [lrange ${:things} 1 end]
+      return $top
+   }
+}
+
+
#
+# Stack of Things
+#
+
+Class Stack
+
+Stack instproc init {} {
+   my instvar things
+   set things ""
+}
+
+Stack instproc push {thing} {
+   my instvar things
+   set things [linsert $things 0 $thing]
+   return $thing
+}
+
+Stack instproc pop {} {
+   my instvar things
+   set top [lindex $things 0]
+   set things [lrange $things 1 end]
+}
+
+
+
+

1.3. Using XOTcl 2.0 and the Next Scripting Language in a Single Interpreter

+

In general, the Next Scripting Framework supports multiple object +systems concurrently. Effectively, every object system has different +base classes for creating objects and classes. Therefore, these object +systems can have different interfaces and names of built-in +methods. Currently, the Next Scripting Framework is packaged with +three object systems:

+
    +
  • +

    +NX +

    +
    • +
  • +

    +XOTcl 2.0 +

    +
    • +
  • +

    +TclCool +

    +
    • +
+

XOTcl 2 is highly compatible with XOTcl 1, the language NX is +described below in more details, the language TclCool was introduced +in Tip#279 and serves primarily an example of a small OO language.

+

A single Tcl interpreter can host multiple Next Scripting Object +Systems at the same time. This fact makes migration from XOTcl to NX +easier. The following example script shows to use XOTcl and NX in a +single script:

+
+
Using Multiple Object Systems in a single Script
+
+
namespace eval mypackage {
+
+  package require XOTcl 2.0
+
+  # Define a class with a public method foo using XOTcl
+  xotcl::Class C1
+  C1 instproc foo {} {puts "hello world"}
+
+  package require nx
+
+  # Define a class with a public method foo using NX
+  nx::Class create C2 {
+    :public method foo {} {puts "hello world"}
+  }
+}
+

One could certainly create object or classes from the different object +systems via fully qualified names (e.g. using e.g. ::xotcl::Class or +::nx::Class), but for migration for systems without explicit +namespaces switching between the object systems eases migration. +"Switching" between XOTcl and NX effectively means the load some +packages (if needed) and to import either the base classes (Object and +Class) of XOTcl or NX into the current namespace.

+
+
+
+
+

2. XOTcl Idioms in the Next Scripting Language

+
+

The following sections are intended for reader familiar with XOTcl and +show, how certain language Idioms of XOTcl can be expressed in NX. In +some cases, multiple possible realizations are listed

+
+

2.1. Defining Objects and Classes

+

When creating objects or classes, one should use the method create +explicitly. In XOTcl, a default unknown method handler was provided for +classes, which create for every unknown method invocation an +object/class with the name of the invoked method. This technique was +convenient, but as well dangerous, since typos in method names lead +easily to unexpected behavior. This default unknown method handler is not +provided in NX (but can certainly be provided as a one-liner in NX by +the application).

+
+ +++ + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
Class ClassName
+
+
Class create ClassName
+
+
Object ObjectName
+
+
Object create ObjectName
+
+
+
+

2.2. Defining Methods

+

In general, both XOTcl and NX support methods on the object level +(per-object methods, i.e. methods only applicable to a single object) +and on the class level (methods inherited to instances of the +classes). While the naming in XOTcl tried to follow closely the Tcl +tradition (using the term proc for functions/methods), NX uses the +term method for defining scripted methods.

+

XOTcl uses the prefix inst to denote that methods are provided for +instances, calling therefore scripted methods for instances +instproc. This is certainly an unusual term. The approach with the +name prefix has the disadvantage, that for every different kind of +method, two names have to be provided (eg. proc and instproc, +forward and instforward).

+

NX on the contrary uses the same term for defining instance method or +object-specific methods. When the term (e.g. method) is used on a +class, the method will be an instance method (i.e. applicable to the +instances of the class). When the term is used on an object with the +modifier object, an object-specific method is defined. This way one +can define the same way object specific methods on an object as well +as on a class.

+

Furthermore, both XOTcl and NX distinguish between scripted methods +(section 3.2.1) and C-defined methods (section 3.2.2). Section 3.2.3 +introduces method protection, which is only supported by NX.

+
+

2.2.1. Scripted Methods Defined in the Init-block of a Class/Object or with Separate Calls

+

The following examples show the definition of a class and its methods +in the init-block of a class (NX only), and the definition of methods +via separate top level calls (XOTcl and NX).

+
+ +++ + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Define instance method 'foo' and object
+# method 'bar' for a Class 'C' with separate
+# toplevel commands
+
+Class C
+C instproc foo args {...}
+C proc bar args {...}
+
+
# Define instance method and object method
+# in the init-block of a class
+
+Class create C {
+  :method foo args {...}
+  :object method bar args {...}
+}
+
+
+
# Define instance method and object method
+# with separate commands
+
+Class create C
+C method foo args {...}
+C object method bar args {...}
+
+
# Define object-specific method foo
+# for an object 'o' with separate commands
+
+Object o
+o set x 1
+o proc foo args {...}
+
+
# Define object method and set
+# instance variable in the init-block of
+# an object
+
+Object create o {
+  set :x 1
+  :object method foo args {...}
+}
+
+
+
# Define object method and set
+# instance variable with separate
+# commands
+
+Object create o
+o eval {set :x 1}
+o object method foo args {...}
+
+
+
+

2.2.2. Different Kinds of Methods

+

This section describes various kinds of methods. The different kinds +of methods are defined via different method-defining methods, which +are summarized in the following table for XOTcl and NX.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Methods for defining methods:
+#
+#     proc
+#     instproc
+#     forward
+#     instforward
+#     parametercmd
+#     instparametercmd
+#
+# All these methods return empty.
+
+
# Methods for defining methods:
+#
+#     alias
+#     forward
+#     method
+#
+# All these methods return method-handles.
+
+

In addition to scripted methods (previous section) XOTcl supports +forwarder (called forward and instforward) and accessor functions +to variables (called parametercmd and instparametercmd). The +accessor functions are used normally internally when object-specific +parameters are defined (see Section 3.4).

+

In NX forwarders are called forward. NX does not provide an public +available method to define variable accessors like parametercmd in +XOTcl, but use internally the Next Scripting Framework primitive +nsf::method::setter when appropriate.

+
+ +++ + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
Class C
+C instforward f1 ...
+C forward f2 ...
+
+Object o
+o forward f3 ...
+
+
# Define forwarder
+
+Class create C {
+  :forward f1 ...
+  :object forward f2 ...
+}
+
+Object create o {
+  :object forward f3 ...
+}
+
+
# Define setter and getter methods in XOTcl.
+#
+# XOTcl provides methods for these.
+
+Class C
+C instparametercmd p1
+C parametercmd p2
+
+Object o
+o parametercmd p3
+
+
# Define setter and getter methods in NX.
+#
+# NX does not provide own methods, but uses
+# the low level framework commands, since
+# application developer will only seldom
+# need it.
+
+Class create C
+::nsf::method::setter C p1
+::nsf::method::setter C -per-object p2
+
+Object create o
+::nsf::method::setter o p3
+
+

NX supports in contrary to XOTcl the method alias which can be used +to register arbitrary Tcl commands or methods for an object or class +under a provided method name. Aliases can be used to reuse a certain implementation in +e.g. different object systems under potentially different names. In +some respects aliases are similar to forwarders, but they do not +involve forwarding overhead.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Method "alias" not available
+
+
# Define method aliases
+# (to scripted or non-scripted methods)
+
+Class create C {
+  :alias a1 ...
+  :object alias a2 ...
+}
+
+Object create o {
+  :object alias a3 ...
+}
+
+
+
+

2.2.3. Method Modifiers and Method Protection

+

NX supports four method modifiers object, public, protected and +private. All method modifiers can be written in front of every +method defining command. The method modifier object is used to denote +object-specific methods (see above). The concept of method protection +is new in NX.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Method modifiers
+#
+#   "object",
+#   "public",
+#   "protected", and
+#   "private"
+#
+# are not available
+
+
# Method modifiers
+#
+#   "object",
+#   "public",
+#   "protected"
+#
+# are applicable for all kinds of
+# method defining methods:
+#
+#    method, forward, alias
+#
+# The modifier "private" is available for
+#
+#    method, forward, alias
+#
+Class create C {
+  :/method-definition-method/ ...
+  :public /method-definition-method/ ...
+  :protected /method-definition-method/ ...
+  :private /method-definition-method/ ...
+  :object /method-definition-method/ ...
+  :public object /method-definition-method/ ...
+  :protected object /method-definition-method/ ...
+  :private object /method-definition-method/ ...
+}
+
+

XOTcl does not provide method protection. In NX, all methods are +defined per default as protected. This default can be changed by the +application developer in various ways. The command ::nx::configure +defaultMethodCallProtection true|false can be used to set the default +call protection for scripted methods, forwarder and aliases. +The defaults can be overwritten also on a class level.

+

NX provides means for method hiding via the method modifier +private. Hidden methods can be invoked only via the -local flag, +which means: "call the specified method defined in the same +class/object as the currently executing method".

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# XOTcl provides no means for
+# method hiding
+
+
# Hiding of methods via "private"
+#
+nx::Class create Base {
+  :private method baz {a b} {expr {$a + $b}}
+  :public method foo {a b} {: -local baz $a $b}
+}
+
+nx::Class create Sub -superclass Base {
+  :public method bar {a b} {: -local baz $a $b}
+  :private method baz {a b} {expr {$a * $b}}
+
+  :create s1
+}
+
+s1 foo 3 4  ;# returns 7
+s1 bar 3 4  ;# returns 12
+s1 baz 3 4  ;# unable to dispatch method 'baz'
+
+
+
+

2.2.4. Method Deletion

+

NX provides an explicit delete method for the deletion of methods.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# XOTcl provides only method deletion with
+# the equivalent of Tcl's "proc foo {} {}"
+/cls/ instproc foo {} {}
+/obj/ proc foo {} {}
+
+
# Deletion of Methods
+#
+/cls/ delete method /name/
+/obj/ delete object method /name/
+
+
+
+
+

2.3. Resolvers

+

The Next Scripting Framework defines Tcl resolvers for method and +variable names to implement object specific behavior. Within the +bodies of scripted methods these resolver treat variable and function +names starting with a colon : specially. In short, a colon-prefixed +variable name refers to an instance variable, and a colon-prefixed +function name refers to a method. The sub-sections below provide +detailed examples.

+

Note that the resolvers of the Next Scripting Framework can be used in +the XOTcl 2.* environment as well.

+
+

2.3.1. Invoking Methods

+

In XOTcl, a method of the same object can be invoked via my, or in +general via using the name of the object in front of the method name.

+

In NX, the own methods are called via the method name prefixed with a +single colon. The invocation of the methods of other objects is the +same in NX and XOTcl.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
Class C
+C instproc foo args {...}
+C instproc bar args {
+  my foo 1 2 3 ;# invoke own method
+  o baz        ;# invoke other object's method
+}
+Object o
+o proc baz {} {...}
+
+
Class create C {
+  :method foo args {...}
+  :method bar args {
+     :foo 1 2 3 ;# invoke own method
+     o baz      ;# invoke other object's method
+  }
+}
+Object create o {
+  :public object method baz {} {...}
+}
+
+
+
+

2.3.2. Accessing Own Instance Variables from Method Bodies

+

In general, the Next Scripting Language favors the access to an +objects’s own instance variables over variable accesses of other +objects. This means that in NX it is syntactically easier to access +the own instance variables. On the contrary, in XOTcl, the variable +access to own and other variables are fully symmetric.

+

In XOTcl, the following approaches are used to access instance +variables:

+
    +
  • +

    +Import instance variables via instvar and access variables via $varName +

    +
    • +
  • +

    +Set or get instance variables via my set varName ?value? or other + variable accessing methods registered on xotcl::Object such as + append, lappend, incr, etc. +

    +
    • +
  • +

    +Register same-named accessor functions and set/get values + of instance variables via my varName ?value? +

    +
    • +
+

In NX, the favored approach to access instance variables is to use +the name resolvers, although it is as well possible to import +variables via nx::var import or to check for the existence of +instance variables via nx::var exists.

+

The following examples summary the use cases for accessing the own and +other instance variables.

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
Class C
+C instproc foo args {
+  # Method scoped variable a
+  set a 1
+  # Instance variable b
+  my instvar b
+  set b 2
+  # Global variable/namespaced variable c
+  set ::c 3
+}
+
+
Class create C {
+  :method foo args {...}
+    # Method scoped variable a
+    set a 1
+    # Instance variable b
+    set :b 2
+    # Global variable/namespaced variable c
+    set ::c 3
+  }
+}
+
+
... instproc ... {
+   my set /varName/ ?value?
+}
+
+
# Set own instance variable to a value via
+# resolver (preferred and fastest way)
+
+... method ... {
+   set :/newVar/ ?value?
+}
+
+
... instproc ... {
+   my instvar /varName/
+   set /varName/ ?value?
+}
+
+
# Set own instance variable via
+# variable import
+
+... method ... {
+   ::nx::var import [self] /varName/
+   set /varName/ ?value?
+}
+
+
... instproc ... {
+   set /varName/ [my set /otherVar/]
+}
+
+
# Read own instance variable
+
+... method ... {
+   set /varName/ [set :/otherVar/]
+}
+
+
+
... method ... {
+   set /newVar/ ${:/otherVar/}
+}
+
+
... instproc ... {
+   my exists /varName/
+}
+
+
# Test existence of own instance variable
+
+... method ... {
+   info :/varName/
+}
+
+
+
 ... method ... {
+   ::nx::var exists [self] /varName/
+}
+
+
+
+

2.3.3. Accessing Instance Variables of other Objects

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/obj/ set /varName/ ?value?
+
+
# Set instance variable of object obj to a
+# value via resolver
+# (preferred way: define property on obj)
+
+/obj/ eval [list set :/varName/ ?value?]
+
+
set /varName/ [/obj/ set /otherVar/]
+
+
# Read instance variable of object obj
+# via resolver
+
+set /varName/ [/obj/ eval {set :/otherVar/}]
+
+
... instproc ... {
+   /obj/ instvar /varName/
+   set /varName/ ?value?
+}
+
+
# Read instance variable of object /obj/
+# via import
+
+... method ... {
+   ::nx::var import /obj/ /varName/
+   set /varName/ ?value?
+}
+
+
/obj/ exists varName
+
+
# Test existence of instance variable of
+# object obj
+
+/obj/ eval {info exists :/varName/}
+
+
+
::nx::var exists /obj/ /varName/
+
+
+
+
+

2.4. Parameters

+

While XOTcl 1 had very limited forms of parameters, XOTcl 2 and NX +provide a generalized and highly orthogonal parameter machinery +handling various kinds of value constraints (also called value +checkers). Parameters are used to specify,

+
    +
  • +

    +how objects and classes are initialized (we call these parameter types + Configure Parameters), and +

    +
    • +
  • +

    +what values can be passed to methods (we call these Method + Parameters). +

    +
    • +
+

Furthermore, parameters might be positional or non-positional, they +might be optional or required, they might have a defined multiplicity, +and value-types, they might be introspected, etc. The Next Scripting +Framework provide a unified, C-implemented infrastructure to handle +both, object and method parameters in the same way with a high degree +of orthogonality.

+

Configuration parameters were specified in XOTcl 1 primarily via the +method parameter in a rather limited way, XOTcl 1 only supported +non-positional parameters in front of positional ones, supported no +value constraints for positional parameters, provided no distinction +between optional and required, and did not support multiplicity.

+

Furthermore, the Next Scripting Framework provides optionally Return +Value Checking based on the same mechanism to check whether some +methods return always the values as specified.

+
+

2.4.1. Parameters for Configuring Objects: Variables and Properties

+

Configure parameters are used for specifying values for configuring +objects when they are created (i.e. how instance variables are +initialized, what parameters can be passed in for initialization, what +default values are used, etc.). Such configuration parameters are +supported in XOTcl primarily via the method parameter, which is used +in XOTcl to define multiple parameters via a list of parameter +specifications.

+

Since the term "parameter" is underspecified, NX uses a more +differentiated terminology. NX distinguishes between configurable +instance variables (also called properties) and non configurable +instance variables (called variables), which might have as well +e.g. default values. The values of configurable properties can be +queried at runtime via cget, and their values can be altered via +configure. When the value of a configure parameter is provided or +changed, the value checkers from the variable definition are used to +ensure, the value is permissible (i.e. it is for example an integer +value). The sum of all configurable object parameters are called +configure parameters. To define a define a configurable variable, NX +uses the method property, for non-configurable variables, the method +variable is used.

+

Optionally, one can define in NX, that a property or a +variable should have a public, protected or private accessor. Such +an accessor is a method with the same name as the variable. In XOTcl, +every parameter defined as well automatically a same-named accessor +method, leading to potential name conflicts with other method names.

+

In the examples below we show the definition of configurable an +non-configurable instance variables using variable and property +respectively.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Define class "Foo" with instance
+# variables "x" and "y" initialized
+# on instance creation. The initialization
+# has to be performed in the constructor.
+
+Class Foo
+Foo instproc init args {
+   instvar x y
+   set x 1
+   set y 2
+}
+
+# Create instance of the class Foo
+Foo f1
+
+# Object f1 has instance variables
+# x == 1 and y == 2
+
+
# Define class "Foo" with instance variables
+# "x" and "y" initialized on instance creation.
+# The method "variable" is similar in syntax
+# to Tcl's "variable" command. During
+# instance creation, the variable
+# definitions are used for the
+# initialization of the variables of the object.
+
+Class create Foo {
+  :variable x 1
+  :variable y 2
+}
+
+# Create instance of the class Foo
+Foo create f1
+
+# Object f1 has instance variables
+# x == 1 and y == 2
+
+

While XOTcl follows a procedural way to initialize variables via the +constructor init, NX follows a more declarative approach. Often, +classes have superclasses, which often want to provide their own +instance variables and default values. The declarative approach from +NX solves this via inheritance, while an procedural approach via +assign statements in the constructor requires explicit constructor +calls, which are often error-prone. Certainly, when a user prefers to +assign initial values to instance variables via explicit assign +operations in constructors, this is as well possible in NX.

+

NX uses the same mechanism to define class variables or object +variables.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# No syntactic support for creating
+# class variables
+
+
+# Define a object variable "V" with value 100 and
+# an instance variable "x". "V" is defined for the
+# class object Foo, "x" is defined in the
+# instances of the class. "object variable" works
+# similar to "object method".
+
+Class create Foo {
+  :object variable V 100
+  :variable x 1
+}
+
+

In the next step, we define configurable instance variables which we +call properties in NX.

+

XOTcl uses the method parameter is a shortcut for creating multiple +configurable variables with automatically created accessors (methods for +reading and writing of the variables). In NX, the preferred way to +create configurable variables is to use the method property. The +method property in NX is similar to variable, but makes the +variables configurable, which means that

+
    +
  1. +

    +one can specify the property as a non-positional parameter upon + creation of the object, +

    +
    2. +
  2. +

    +one can query the value via the method cget, and +

    +
    3. +
  3. +

    +one can modify the value of the underlying variable via the method + configure. +

    +
    4. +
+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Parameters specified as a list
+# (short form); parameter
+# "a" has no default, "b" has default "1"
+
+Class Foo -parameter {a {b 1}}
+
+# Create instance of the class Foo
+Foo f1 -a 0
+
+# Object f1 has instance variables
+# a == 0 and b == 1
+
+# XOTcl registers automatically accessors
+# for the parameters. Use the accessor
+# "b" to output the value of variable "b"
+puts [f1 b]
+
+# Use the setter to alter value of
+# instance variable "b"
+f1 b 100
+
+
# Define property "a" and "b". The
+# property "a" has no default, "b" has
+# default value "1"
+
+Class create Foo {
+  :property a
+  :property {b 1}
+}
+
+# Create instance of the class Foo
+Foo create f1 -a 0
+
+# Object f1 has instance variables
+# a == 0 and b == 1
+
+# Use the method "cget" to query the value
+# of a configuration parameter
+puts [f1 cget -b]
+
+# Use the method "configure" to alter the
+# value of instance variable "b"
+f1 configure -b 100
+
+

In general, NX allows to create variables and properties with and +without accessor methods. The created accessor methods might be +public, protected or public. When the value none is provided +to -accessor, no accessor will be created. This is actually the +default in NX. In order to change the default behavior in NX, one can use +::nx::configure defaultAccessor none|public|protected|private.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# "parameter" creates always accessor
+# methods, accessor methods are
+# always public, no "cget" is available.
+
+Class create Foo -parameter {a {b1}}
+
+# Use the accessor method to query
+# the value of a configuration parameter
+puts [f1 b]
+
+# Use the accessor method to set the
+# value of instance variable "a"
+f1 a 100
+
+# Use the accessor method to unset the
+# value of instance variable "a" n.a. via
+# accessor
+
+
# Define property "a" and "b". The
+# property "a" has no default, "b" has
+# default value "1"
+
+Class create Foo {
+  :variable -accessor public a
+  :property -accessor public {b 1}
+}
+
+# Use the accessor method to query
+# the value of a configuration parameter
+puts [f1 b get]
+
+# Use the accessor method to set the
+# value of instance variable "a"
+f1 a set 100
+
+# Use the accessor method to unset the
+# value of instance variable "a"
+f1 a unset
+
+

Similar to variable, properties can be defined in NX on the class +and on the object level.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# XOTcl provides no means to define
+# configurable variables at the object
+# level
+
+
# Define class with a property for the class object
+# named "cp". This is similar to "static variables"
+# in some other object-oriented programming
+# languages.
+
+Class create Foo {
+  ...
+  :object property cp 101
+}
+
+# Define object property "op"
+
+Object create o {
+  :object property op 102
+}
+
+

NX supports value constraints (value-checkers) for object and method +parameters in an orthogonal manner. NX provides a predefined set of +value checkers, which can be extended by the application developer. +In NX, the value checking is optional. This means that it is possible to +develop e.g. which a large amount of value-checking and deploy the +script with value checking turned off, if the script is highly +performance sensitive.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# No value constraints for
+# parameter available
+
+
# Predefined value constraints:
+#    object, class, alnum, alpha, ascii, boolean,
+#    control, digit, double, false, graph, integer,
+#    lower, parameter, print, punct, space, true,
+#    upper, wordchar, xdigit
+#
+# User defined value constraints are possible.
+# All parameter value checkers can be turned on
+# and off at runtime.
+#
+# Define a required boolean property "a"
+# and an integer property "b" with a default.
+# The first definition uses "properties",
+# the second definition uses multiple
+# "property" statements.
+
+Class create Foo -properties {
+   a:boolean
+   {b:integer 1}
+}
+
+
+
Class create Foo {
+   :property a:boolean
+   :property {b:integer 1}
+}
+
+

In XOTcl all configure parameters were optional. Required parameters have +to be passed to the constructor of the object.

+

NX allows to define optional and required configure parameters (as +well as method parameters). Therefore, configure parameters can be used +as the single mechanism to parametrize objects. It is in NX not +necessary (and per default not possible) to pass arguments to the +constructor.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Required parameter not available
+
+
# Required parameter:
+# Define a required property "a" and a
+# required boolean property "b"
+
+Class create Foo -properties {
+   a:required
+   b:boolean,required
+}
+
+
+
+Class create Foo {
+   :property a:required
+   :property b:boolean,required
+}
+
+

NX supports in contrary to XOTcl to define the multiplicity of values +per parameter. In NX, one can specify that a parameter can accept the +value "" (empty) in addition to e.g. an integer, or one can specify that the +value is an empty or non-empty ist of values via the multiplicity. For +every specified value, the value checkers are applied.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Multiplicity for parameter
+# not available
+
+
# Parameter with multiplicity
+#   ints is a list of integers, with default
+#   objs is a non-empty list of objects
+#   obj is a single object, maybe empty
+
+Class create Foo -properties {
+  {ints:integer,0..n ""}
+   objs:object,1..n
+   obj:object,0..1
+}
+
+
+
Class create Foo {
+  :property {ints:integer,0..n ""}
+  :property objs:object,1..n
+  :property obj:object,0..1
+}
+
+

For the implementation of variables and properties, NX uses slot +objects, which are an extension to the -slots already available in +XOTcl. While very for every property in NX, a slot object is created, +for performance reasons, not every variable has a slot associated.

+

When an property is created, NX does actually three things:

+
    +
  1. +

    +Create a slot object, which can be specified in more detail + using the init-block of the slot object +

    +
    2. +
  2. +

    +Create a parameter definition for the initialization of the + object (usable via a non-positional parameter during object + creation), and +

    +
    3. +
  3. +

    +register optionally an accessor function (setter), for which the usual + protection levels (public, protected or private) can be used. +

    +
    4. +
+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Define parameters via slots
+
+Class Foo -slots {
+   Attribute a
+   Attribute b -default 1
+}
+
+# Create instance of the class Foo
+# and provide a value for instance
+# variable "a"
+Foo f1 -a 0
+
+# Object f1 has a == 0 and b == 1
+
+
# Configurable parameters specified via the
+# method "property" (supports method
+# modifiers and scripted configuration;
+# see below)
+
+Class create Foo {
+   :property a
+   :property {b 1}
+}
+
+# Create instance of the class Foo and
+# provide a value for instance variable "a"
+Foo create f1 -a 0
+
+# Object f1 has a == 0 and b == 1
+
+

Since the slots are objects, the slot objects can be configured and +parametrized like every other object in NX. Slot objects can be +provided with a scripted initialization as well. We show first the +definition of properties similar to the functionality provided as well +by XOTcl and show afterwards how to use value constraints, optional +parameters, etc. in NX.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Define parameter with an an
+# attribute-specific type checker
+
+Class Person -slots {
+  Attribute create sex -type "sex" {
+    my proc type=sex {name value} {
+      switch -glob $value {
+        m* {return m}
+        f* {return f}
+        default {
+          error "expected sex but got $value"
+        }
+      }
+    }
+  }
+}
+
+
# Configure parameter with scripted
+# definition (init-block), defining a
+# property specific type checker
+
+Class create Person {
+    :property -accessor public sex:sex,convert {
+
+      # define a converter to standardize representation
+      :object method type=sex {name value} {
+        switch -glob $value {
+          m* {return m}
+          f* {return f}
+          default {error "expected sex but got $value"}
+        }
+      }
+
+    }
+}
+
+

The parameters provided by a class for the initialization of +instances can be introspected via querying the parameters +of the method create: /cls/ info lookup parameters create +(see [info_configure_parameter]).

+
+
+

2.4.2. Delete Variable Handlers

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# No syntactic support for deleting
+# variable handlers
+
+
# Like deletion of Methods:
+# Delete on the object, where the
+# variable handler is defined.
+
+/cls/ delete property /name/
+/obj/ delete object property /name/
+
+/cls/ delete variable /name/
+/obj/ delete object variable /name/
+
+
+
+

2.4.3. Method Parameters

+

Method parameters are used to specify the interface of a single method +(what kind of values may be passed to a method, what default values +are provided etc.). The method parameters specifications in XOTcl 1 +were limited and allowed only value constraints for non positional +arguments.

+

NX and XOTcl 2 provide value constraints for all kind of method parameters. +While XOTcl 1 required non-positional arguments to be listed in front of +positional arguments, this limitation is lifted in XOTcl 2.

+
+ +++ + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Define method foo with non-positional
+# parameters (x, y and y) and positional
+# parameter (a and b)
+
+Class C
+C instproc foo {
+   -x:integer
+   -y:required
+   -z
+   a
+   b
+} {
+   # ...
+}
+C create c1
+
+# invoke method foo
+c1 foo -x 1 -y a 2 3
+
+
# Define method foo with
+# non-positional parameters
+# (x, y and y) and positional
+# parameter (a and b)
+
+Class create C {
+   :public method foo {
+      -x:integer
+      -y:required
+      -z
+      a
+      b
+   } {
+      # ...
+   }
+   :create c1
+}
+# invoke method foo
+c1 foo -x 1 -y a 2 3
+
+
# Only leading non-positional
+# parameters are available; no
+# optional positional parameters,
+# no value constraints on
+# positional parameters,
+# no multiplicity, ...
+
+
# Define various forms of parameters
+# not available in XOTcl 1
+
+Class create C {
+  # trailing (or interleaved) non-positional
+  # parameters
+  :public method m1 {a b -x:integer -y} {
+    # ...
+  }
+
+  # positional parameters with value constraints
+  :public method m2 {a:integer b:boolean} {
+    #...
+  }
+
+  # optional positional parameter (trailing)
+  :public method set {varName value:optional} {
+    # ....
+  }
+
+  # parameter with multiplicity
+  :public method m3 {-objs:object,1..n c:class,0..1} {
+    # ...
+  }
+
+  # In general, the same list of value
+  # constraints as for configure parameter is
+  # available (see above).
+  #
+  # User defined value constraints are
+  # possible. All parameter value checkers
+  # can be turned on and off.
+}
+
+
+
+

2.4.4. Return Value Checking

+

Return value checking is a functionality available in the Next +Scripting Framework, that was not yet available in XOTcl 1. A return +value checker assures that a method returns always a value satisfying +some value constraints. Return value checkers can be defined on all +forms of methods (scripted or C-implemented). Like for other value +checkers, return value checkers can be turned on and off.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# No return value checking
+# available
+
+
# Define method foo with non-positional
+# parameters (x, y and y) and positional
+# parameter (a and b)
+
+Class create C {
+
+  # Define method foo which returns an
+  # integer value
+  :method foo -returns integer {-x:integer} {
+    # ...
+   }
+
+  # Define an alias for the Tcl command ::incr
+  # and assure, it always returns an integer
+  # value
+  :alias incr -returns integer ::incr
+
+  # Define a forwarder that has to return an
+  # integer value
+  :forward ++ -returns integer ::expr 1 +
+
+ # Define a method that has to return a
+ # non-empty list of objects
+ :public object method instances {} \
+    -returns object,1..n {
+   return [:info instances]
+  }
+}
+
+
+
+
+

2.5. Interceptors

+

XOTcl and NX allow the definition of the same set of interceptors, +namely class- and object-level mixins and class- and object-level +filters. The primary difference in NX is the naming, since NX abandons +the prefix "inst" from the names of instance specific method, but uses +the modifier object" for object specific methods.

+

Therefore, in NX, if a mixin is registered on a class-level, it is +applicable for the instances (a per-class mixin), and if and object +mixin is registered, it is a per-object mixin. In both cases, the +term mixin is used, in the second case with the modifier +object. As in all other cases, one can register the same way a +per-object mixin on a plain object or on a class object.

+
+

2.5.1. Register Mixin Classes and Mixin Guards

+
+ +++ + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/cls/ instmixin ...
+/cls/ instmixinguard /mixin/ ?condition?
+
+# Query per-class mixin
+/cls/ instmixin
+
+
# Register/clear per-class mixin and guard for
+# a class
+
+/cls/ mixins add|set|clear ...
+/cls/ mixins guard /mixin/ ?condition?
+/cls/ configure -mixin ...
+
+# Query per-class mixins
+/cls/ mixins get
+/cls/ cget -mixins
+
+# Query per-class mixins (without guards)
+/cls/ mixins classes
+
+
/obj/ mixin ...
+/obj/ mixinguard /mixin/ ?condition?
+
+# Query per-object mixins
+/obj/ mixin
+
+
# Register/clear per-object mixin and guard for
+# an object
+
+/obj/ object mixins add|set|clear ...
+/obj/ object mixins guard /mixin/ ?condition?
+/obj/ configure -object-mixins ...
+
+# Query per-object mixin
+/obj/ object mixins get
+/obj/ cget -object-mixin
+
+# Query per-object mixins (without guards)
+/cls/ mixins classes
+
+
+
+

2.5.2. Register Filters and Filter Guards

+
+ +++ + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# Register per-class filter and guard for
+# a class
+/cls/ instfilter ...
+/cls/ instfilterguard /filter/ ?condition?
+
+# Query per-class filter
+/cls/ instfilter
+
+
# Register/clear per-class filter and guard for
+# a class
+
+/cls/ filters add|set|clear ...
+/cls/ filters guard /filter/ ?condition?
+/cls/ configure -filters ...
+
+# Query per-class filters
+/cls/ filters get
+/cls/ cget -filters
+
+# Query per-class filters (without guards)
+/cls/ filters methods
+
+
/obj/ filter ...
+/obj/ filterguard /filter/ ?condition?
+
+
# Register(clear per-object filter and guard for
+# an object
+
+/obj/ object filters add|set|clear ...
+/obj/ object filters guard /filter/ ?condition?
+/obj/ configure -object-filters ...
+
+# Query per-object filters
+/cls/ object filters get
+/obj/ cget -object-filters
+
+# Query per-object filters (without guards)
+/cls/ object filters methods
+
+
+
+
+

2.6. Introspection

+

In general, introspection in NX became more orthogonal and less +dependent on the type of the method. In XOTcl it was e.g. necessary +that a developer had to know, whether a method is e.g. scripted or not +and has to use accordingly different sub-methods of info.

+

In NX, one can use e.g. always info method with a subcommand and the +framework tries to hide the differences as far as possible. So, one +can for example obtain with info method parameter the parameters of +scripted and C-implemented methods the same way, one can get the +definition of all methods via info method definition and one can get +an manual-like interface description via info method +syntax. In addition, NX provides means to query the type of +a method, and NX allows to filter by the type of the method.

+
+

2.6.1. List sub- and superclass relations

+

While XOTcl used singular words for introspecting sub- and superclass +relations, NX uses plural word to indicate that potentially a list of +values is returned.

+
+ +++ + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/cls/ info superclass ?pattern?
+
+
/cls/ info superclasses ?pattern?
+
+
/cls/ info subclass ?pattern?
+
+
/cls/ info subclasses -type setter ?pattern?
+
+
+
+

2.6.2. List methods defined by classes

+

While XOTcl uses different names for obtaining different kinds of +methods defined by a class, NX uses info methods in an orthogonal +manner. NX allows as well to use the call protection to filter the +returned methods.

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/cls/ info instcommands ?pattern?
+
+
/cls/ info methods ?pattern?
+
+
/cls/ info instparametercmd ?pattern?
+
+
/cls/ info methods -type setter ?pattern?
+
+
/cls/ info instprocs ?pattern?
+
+
/cls/ info methods -type scripted ?pattern?
+
+
# n.a.
+
+
/cls/ info methods -type alias ?pattern?
+/cls/ info methods -type forwarder ?pattern?
+/cls/ info methods -type object ?pattern?
+/cls/ info methods -callprotection public|protected ...
+
+
+
+

2.6.3. List methods defined by objects

+

While XOTcl uses different names for obtaining different kinds of +methods defined by an object, NX uses info methods in an orthogonal +manner. NX allows as well to use the call protection to filter the +returned methods.

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/obj/ info commands ?pattern?
+
+
/obj/ info object methods ?pattern?
+
+
/obj/ info parametercmd ?pattern?
+
+
/obj/ info object methods -type setter ?pattern?
+
+
/obj/ info procs ?pattern?
+
+
/obj/ info object methods -type scripted ?pattern?
+
+
# n.a.
+
+
/obj/ info object methods -type alias ?pattern?
+/obj/ info object methods -type forwarder ?pattern?
+/obj/ info object methods -type object ?pattern?
+/obj/ info object methods -callprotection public|protected ...
+
+
+
+

2.6.4. Check existence of a method

+

NX provides multiple ways of checking, whether a method exists; one +can use info method exists to check, if a given method exists +(return boolean), or one can use info methods ?pattern?, where +pattern might be a single method name without wild-card +characters. The method info methods ?pattern? returns a list of +matching names, which might be empty. These different methods appear +appropriate depending on the context.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/obj|cls/ info \
+   [inst](commands|procs|parametercmd) \
+   ?pattern?
+
+
/cls/ info method exists /methodName/
+/cls/ info methods /methodName/
+/obj/ info object method exists /methodName/
+/obj/ info object methods /methodName/
+
+
+
+

2.6.5. List callable methods

+

In order to obtain for an object the set of artefacts defined in the + class hierarchy, NX uses info lookup. One can either lookup methods + (via info lookup methods) or slots (via info lookup slots). The + plural term refers to a potential set of return values.

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/obj/ info methods ?pattern?
+
+
/obj/ info lookup methods ... ?pattern?
+# Returns list of method names
+
+
# n.a.
+
+
# List only application specific methods
+/obj/ info lookup methods -source application ... ?pattern?
+# Returns list of method names
+
+
# Options for 'info methods'
+#
+# -incontext
+# -nomixins
+
+
# Options for 'info lookup methods'
+#
+# -source ...
+# -callprotection ...
+# -incontext
+# -type ...
+# -nomixins
+
+
# n.a.
+
+
# List slot objects defined for obj
+# -source might be all|application|baseclasses
+# -type is the class of the slot object
+
+/obj/ info lookup slots ?-type ...? ?-source ...? ?pattern?
+
+# Returns list of slot objects
+
+
# List registered filters
+/obj/ info filters -order ?-guards? ?pattern?
+
+# List registered mixins
+/obj/ info mixins -heritage ?-guards? ?pattern?
+
+
# List registered filters
+/obj/ info lookup filters ?-guards? ?pattern?
+
+# List registered mixins
+/obj/ info lookup mixins ?-guards? ?pattern?
+
+
+
+

2.6.6. List object/class where a specified method is defined

+

info lookup can be used as well to determine, where exactly an + artefact is located. One can obtain this way a method handle, where +a method or filter is defined.

+

The concept of a method-handle is new in NX. The method-handle +can be used to obtain more information about the method, such as +e.g. the definition of the method.

+
+ +++ + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/obj/ procsearch /methodName/
+
+
/obj/ info lookup method /methodName/
+# Returns method-handle
+
+
/obj/ filtersearch /methodName/
+
+
/obj/ info lookup filter /methodName/
+# Returns method-handle
+
+
+
+

2.6.7. List definition of scripted methods

+

XOTcl contains a long list of info subcommands for different kinds of +methods and for obtaining more detailed information about these +methods.

+

In NX, this list of info subcommands is much shorter and more +orthogonal. For example info method definition can be used to obtain +with a single command the full definition of a scripted method, and +furthermore, it works as well the same way to obtain e.g. the +definition of a forwarder or an alias.

+

While XOTcl uses different names for info options for objects and +classes (using the prefix "inst" for instance specific method), NX +uses for object specific method the modifier object. For definition +of class object specific methods, use the modifier object as usual.

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# n.a.
+
+
/cls/ info method definition /methodName/
+/obj/ info object method definition /methodName/
+
+
/cls/ info instbody /methodName/
+/obj/ info body /methodName/
+
+
/cls/ info method body /methodName/
+/obj/ info object method body /methodName/
+
+
/cls/ info instargs /methodName/
+/obj/ info args /methodName/
+
+
/cls/ info method args /methodName/
+/obj/ info object method args /methodName/
+
+
/cls/ info instnonposargs /methodName/
+/obj/ info object method args /methodName/
+
+
/cls/ info method parameter /methodName/
+/obj/ info object method parameter /methodName/
+
+
/cls/ info instdefault /methodName/
+/obj/ info default /methodName/
+
+
# not needed, part of
+# "info ?object? method parameter"
+
+
/cls/ info instpre /methodName/
+/obj/ info pre /methodName/
+
+
/cls/ info method precondition /methodName/
+/obj/ info object method precondition /methodName/
+
+
/cls/ info instpost /methodName/
+/obj/ info post /methodName/
+
+
/cls/ info method postcondition /methodName/
+/obj/ info object method postcondition /methodName/
+
+

Another powerful introspection option in NX is info ?object? method +syntax which obtains a representation of the parameters of a +method in the style of Tcl man pages (regardless of the kind of +method).

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# n.a.
+
+
/cls/ info method syntax /methodName/
+/obj/ info object method syntax /methodName/
+
+
+
+

2.6.8. List Configure Parameters

+

The way, how newly created objects can be configured is determined in NX +via properties. The configuration happens during creation via the +methods create or new or during runtime via configure. These +methods have therefore virtual argument lists, depending on the object +or class on which they are applied.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# n.a.
+
+
# Return the parameters applicable to
+# the create method of a certain class.
+# class can be configured. A pattern can
+# be used to filter the results.
+
+/cls/ info lookup parameters create ?/pattern/?
+
+# Return in the result in documentation syntax
+
+/cls/ info lookup syntax create ?/pattern/?
+
+# "info lookup parameters configure" returns
+# parameters available for configuring the
+# current object  (might contain object
+# specific information)
+
+/obj/ info lookup parameters configure ?pattern?
+
+# "info lookup configure syntax" returns syntax of
+# a call to configure in the Tcl parameter syntax
+
+/obj/ info lookup syntax configure
+
+# Obtain information from a parameter
+# (as e.g. returned from "info lookup
+# parameters configure").
+
+nsf::parameter::info name /parameter/
+nsf::parameter::info syntax /parameter/
+nsf::parameter::info type /parameter/
+
+
+
+

2.6.9. List Variable Declarations (property and variable)

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# obtain parameter definitions defined
+# for a class
+/cls/ info parameter
+
+
# "info variables" returns handles of
+# properties and variables defined by this
+# class or object
+
+/cls/ info variables ?pattern?
+/obj/ info object variables ?pattern?
+
+# "info lookup variables" returns handles
+# of variables and properties applicable
+# for the current object (might contain
+# object specific information)
+
+/obj/ info lookup variables /pattern/
+
+# "info variable" lists details about a
+# single property or variable.
+
+/obj/ info variable definition /handle/
+/obj/ info variable name /handle/
+/obj/ info variable parameter /handle/
+
+
+
+

2.6.10. List Slots

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# n.a.
+
+
# Return list of slots objects defined on the
+# object or class
+#
+# -source might be all|application|baseclasses
+# -type is the class of the slot object
+# -closure includes slots of superclasses
+
+/cls/ info slots \
+   ?-type value? ?-closure? ?-source value? ?pattern?
+/obj/ info object slots ?-type ...? ?pattern?
+
+# List reachable slot objects defined for obj
+# -source might be all|application|baseclasses
+# -type is the class of the slot object
+# Returns list of slot objects.
+
+/obj/ info lookup slots \
+   ?-type ...? ?-source ... ?pattern?
+
+# Obtain definition, name or parameter from
+# slot object
+
+/slotobj/ definition
+/slotobj/ name
+/slotobj/ parameter
+
+
+
+

2.6.11. List Filter or Mixins

+

In NX all introspection options for filters are provided via +info filters and all introspection options for mixins are +provided via info mixins.

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/obj/ info filter ?-guards? ?-order? ?pattern?
+/obj/ info filterguard /name/
+
+
/obj/ info object filters \
+   ?-guards? ?pattern?
+
+
/cls/ info instfilter \
+   ?-guards? ?-order? ?pattern?
+/cls/ info instfilterguard /name/
+
+
/cls/ info filters \
+   ?-guards? ?pattern?
+
+
/obj/ info mixin ?-guards? ?-order ?pattern?
+/obj/ info mixinguard /name/
+
+
/obj/ info object mixins \
+   ?-guards? ?pattern?
+
+
/cls/ info instmixin \
+   ?-guards? ?-order? ?pattern?
+/cls/ info instmixinguard /name/
+
+
/cls/ info mixins \
+   ?-closure? ?-guards? ?-heritage? ?pattern?
+
+
+
+

2.6.12. List definition of methods defined by aliases, setters or forwarders

+

As mentioned earlier, info method definition can be used on every +kind of method. The same call can be used to obtain the definition of +a scripted method, a method-alias, a forwarder or a setter method.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# n.a.
+
+
/cls/ info method definition /methodName/
+/obj/ info object method definition /methodName/
+
+
+
+

2.6.13. List Method-Handles

+

NX supports method-handles to provide means to obtain further +information about a method or to change maybe some properties of a +method. When a method is created, the method creating method returns +the method handle to the created method.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# n.a.
+
+
#
+# List the method handle of the specified method,
+# can be used e.g. for aliases. "handle" is the short
+# form of "definitionhandle".
+#
+/cls/ info method handle /methodName/
+/obj/ info object method handle /methodName/
+#
+# For ensemble methods (method name contains
+# spaces) one can query as well the registration
+# handle, which is the handle to the root of the
+# ensemble; the definition handle points to the
+# leaf of the ensemble.
+#
+/cls/ info method registrationhandle /methodName/
+/obj/ info object method registrationhandle /methodName/
+#
+# For aliases, one can query the original
+# definition via "info method origin"
+#
+/cls/ info method origin /methodName/
+/obj/ info object method origin /methodName/
+
+
+
+

2.6.14. List type of a method

+

The method info ?object? method type is new in NX to obtain the type of the +specified method.

+
+ +++ + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
# n.a.
+
+
/cls/ info method type /methodName/
+/obj/ info object method type /methodName/
+
+
+
+

2.6.15. List the scope of mixin classes

+

NX provides a richer set of introspection options to obtain +information, where mixins classes are mixed into.

+
+ +++ + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/cls/ info mixinof ?-closure? ?pattern?
+
+
# List objects, where /cls/ is a
+# per-object mixin
+
+/cls/ info mixinof -scope object ?-closure? \
+   ?pattern?
+
+
/cls/ info instmixinof ?-closure? ?pattern?
+
+
# List classes, where /cls/ is a per-class mixin
+
+/cls/ info mixinof -scope class ?-closure? \
+   ?pattern?
+
+
# n.a.
+
+
# List objects and classes, where /cls/ is
+# either a per-object or a per-class mixin
+
+/cls/ info mixinof -scope all ?-closure? \
+   ?pattern?
+
+
+
/cls/ info mixinof ?-closure? ?pattern?
+
+
+
+

2.6.16. Check properties of object and classes

+

Similar as noted before, NX uses rather a hierarchical approach of +naming using multiple layers of subcommands).

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/obj/ istype /sometype/
+
+
# Check if object is a subtype of some class
+/obj/ info has type /sometype/
+
+
/obj/ ismixin /cls/
+
+
# Check if object has the specified mixin registered
+/obj/ info has mixin /cls/
+
+
/obj/ isclass ?/cls/?
+
+
# Check if object is an NX class
+/obj/ has type ::nx::Class
+
+# Check if object is a class in one of the
+# NSF object systems
+::nsf::is class /obj/
+
+
/obj/ ismetaclass /cls/
+
+
# Check if class is an NX metaclass
+expr {[/cls/ info heritage ::nx::Class] ne ""}
+
+# Check if object is a metaclass in one of the
+# NSF object systems
+::nsf::is metaclass /obj/
+
+
# n.a.
+
+
# Check if object is a baseclass of an object system
+::nsf::is baseclass /obj/
+
+
# n.a.
+
+
# Return name of object (without namespace prefix)
+/obj/ info name
+
+
/obj/ object::exists /obj/
+
+
# Check for existence of object (nsf primitive)
+::nsf::object::exists /obj/
+
+
+
+

2.6.17. Call-stack Introspection

+

Call-stack introspection is very similar in NX and XOTcl. NX uses for +subcommand the term current instead of self, since self has a +strong connotation to the current object. The term proc is renamed +by method.

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
self
+
+
self
+
+
+
current object
+
+
self class
+
+
current class
+
+
self args
+
+
current args
+
+
self proc
+
+
current method
+
+
self callingclass
+
+
current calledclass
+
+
self callingobject
+
+
current callingobject
+
+
self callingproc
+
+
current callingmethod
+
+
self calledclass
+
+
current calledclass
+
+
self calledproc
+
+
current calledmethod
+
+
self isnextcall
+
+
current isnextcall
+
+
self next
+
+
# Returns method-handle of the
+# method to be called via "next"
+current next
+
+
self filterreg
+
+
# Returns method-handle of the
+# filter method
+current filterreg
+
+
self callinglevel
+
+
current callinglevel
+
+
self activelevel
+
+
current activelevel
+
+
+
+
+

2.7. Other Predefined Methods

+
+ +++ + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/obj/ requireNamespace
+
+
/obj/ require namespace
+
+
# n.a.
+
+
/obj/ require method
+
+
+
+

2.8. Dispatch, Aliases, etc.

+

todo: to be done or omitted

+
+
+

2.9. Assertions

+

In contrary to XOTcl, NX provides no pre-registered methods for +assertion handling. All assertion handling can e performed via the +Next Scripting primitive nsf::method::assertion.

+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
XOTcl Next Scripting Language
+
+
/obj/ check /checkoptions/
+
+
::nsf::method::assertion /obj/ check /checkoptions/
+
+
/obj/ info check
+
+
::nsf::method::assertion /obj/ check
+
+
/obj/ invar /conditions/
+
+
::nsf::method::assertion /obj/ object-invar /conditions/
+
+
/obj/ info invar
+
+
::nsf::method::assertion /obj/ object-invar
+
+
/cls/ instinvar /conditions/
+
+
::nsf::method::assertion /cls/ class-invar /conditions/
+
+
/cls/ info instinvar
+
+
::nsf::method::assertion /cls/ class-invar
+
+
/cls/ invar /conditions/
+
+
::nsf::method::assertion /cls/ object-invar /conditions/
+
+
/cls/ info invar
+
+
::nsf::method::assertion /cls/ object-invar
+
+
+
+

2.10. Method Protection

+

As described above, NX supports method +protection via the method modifiers protected and public. A +protected method can be only called from an object of that class, +while public methods can be called from every object. The method +protection can be used to every kind of method, such as e.g. scripted +methods, aliases, forwarders, or accessors. For invocations, +the most specific definition (might be a mixin) is used for +determining the protection.

+
+
+
+
+

3. Incompatibilities between XOTcl 1 and XOTcl 2

+
+
+

3.1. Resolvers

+

The resolvers (variable resolvers, function resolvers) of the Next +Scripting Framework are used as well within XOTcl 2. When variable +names or method names starting with a single colon are used in XOTcl 1 +scripts, conflicts will arise with the resolver. These names must be +replaced.

+
+
+

3.2. Parameters

+

The following changes for parameters could be regarded as bug-fixes.

+
+

3.2.1. Parameter usage without a value

+

In XOTcl 1, it was possible to call a parameter method during object +creation via the dash-interface without a value (in the example below -x).

+
+
+
# XOTcl example
+
+Class Foo -parameter {x y}
+Foo f1 -x -y 1
+

Such cases are most likely mistakes. All parameter configurations in XOTcl 2 require an argument.

+
+
+

3.2.2. Ignored Parameter definitions

+

In XOTcl 1, a more specific parameter definition without a default was ignored +when a more general parameter definition with a default was +present. In the example below, the object b1 contained in XOTcl 1 +incorrectly the parameter x (set via default from Foo), while in +XOTcl 2, the variable won’t be set.

+
+
+
# XOTcl example
+
+Class Foo -parameter {{x 1}}
+Class Bar -superclass Foo -parameter x
+Bar b1
+
+
+

3.2.3. Changing classes and superclasses

+

NX does not define the methods class and superclass (like XOTcl), but allows to +alter all object/class relations (including +class/superclass/object-mixin/…) +nsf::relation::set. The class and superclass can be certainly queried +in all variants with info class or info superclasses.

+
+
+
# NX example
+
+nx::Class create Foo
+Foo create f1
+
+# now alter the class of object f1
+nsf::relation::set f1 class ::nx::Object
+
+
+

3.2.4. Overwriting procs/methods with objects and vice versa

+

NSF is now more conservative on object/method creation. In contrary to +XOTcl 1 NSF does not allow to redefined a pre-existing command +(e.g. "set") with an object and vice versa. Like in XOTcl 1, +preexisting objects and classes con be redefined (necessary for +reloading objects/classes in an running interpreter).

+
+
+

3.2.5. Info heritage

+

info heritage returns in XOTcl 1 the transitive superclass +hierarchy, which is equivalent with info superclasses -closure and +therefore not necessary. In XOTcl 2 (and NX), info heritage includes +as well the transitive per-class mixins.

+
+
+
+

3.3. Slots

+

All slot objects (also XOTcl slot objects) are now next-scripting +objects of baseclass ::nx::Slot. The name of the experimental +default-setter initcmd was changed to defaultcmd. Code directly +working on the slots objects has to be adapted.

+
+
+

3.4. Obsolete Commands

+

Parameter-classes were rarely used and have been replaced by the more +general object parametrization. Therefore, cl info parameterclass has +been removed.

+
+
+

3.5. Stronger Checking

+

The Next Scripting Framework performs stronger checking than XOTcl 1 +For example, the requiredness of slots in XOTcl 1 was just a +comment, while XOTcl 2 enforces it.

+
+
+

3.6. Exit Handlers

+

The exit hander interface changed from a method of ::xotcl::Object +into the Tcl command ::nsf::exithandler:

+
+
+
# NX example
+::nsf::exithandler set|get|unset ?arg?
+
+
+
+
+
+ + +