1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + | Class create Foo { + + :method foo args {...} + # Method scoped variable a + set a 1 + # Instance variable b + set :b 2 + # Global variable/namespaced variable c + set ::c 3 + } +} |
The method pop returns the most recently stacked element and removes it from the stack. Therefore, it takes the first element from the list (using the Tcl command lindex), assigns it to the method-scoped @@ -1509,9 +1509,324 @@
3. Basic Language Features of NX
-
+
+
+
+
+3.1. Parameters
+3.1. Variables and Properties
+In general, NX does not need variable declarations. It allows to +create, modify or variables on the fly by using e.g. the Tcl commands +set and unset. Depending on the variable name (or more precisely, +depending on the prefix consisting of colons :), a variable is +either local to a method, or an instance variable, or a global +variable. The rules are:
-
+
-
+
+A variable without any colon prefix refers typically to a + method scoped variable (the variable is created at the begin of the + invocation of the method and deleted, when the method ends); + In the example below, the variable a is method scoped. +
+
+ -
+
+A variable with a single colon prefix refers to an instance variable + (the variable is part of the object, when the object is destroyed, + the variable is deleted as well. In the example below, the variable + b is an instance variable. +
+
+ -
+
+a variable with two leading colons refers to a global variable (the + lifespan ends when te variable is explicitly unset or the script + ends). Also variables in placed in Tcl namespaces are global + variables. In the example below, the variable c is a global + variable. +
+
+
Listing 16: Scopes of Variables
+
+
+
Listing 16 shows a method foo +of some class Foo referring to differently scoped variables.
+
+
+
+
+
+
+
+
+3.1.1. Properties: Instance Variables with Accessors
+So, in general, there is no need to define or declare instance +variables in NX. However, in some cases, a definition is useful. For +example, one can define properties on classes, which are inherited to +subclasses, and which are used during object initialization. Consider +the following example:
Listing 17: Properties
+
+
+
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20 + 21 + 22 + 23 + 24 + 25 + 26 + 27 + | # +# Define a class Person with properties "name" +# and "birthday" +# +nx::Class create Person { + :property name:required + :property birthday +} + +# +# Define a class Student as specialization of Person +# with additional properties +# +nx::Class create Student -superclass Person { + :property matnr:required + :property {oncampus:boolean true} +} + +# +# Create instances using object parameters +# for the initialization +# +Person create p1 -name Bob +Student create s1 -name Susan -matnr 4711 + +# Access property value via accessor method +puts "The name of s1 is [s1 name]" |
We define here a class named Person with two properties, namely + name and birthday.
We refer with the term property to an instance variable with +accessors, where the property definition might carry as well +value-constraints and a default value.
When the class Person is defined, NX provides as well automatically +accessors. Accessors are methods named like the variables, which are +used to access (to read and write) the underlying instance +variables. Therefore, in our example, the class Person has two +methods implied by the property definition, namely the method name +and the method birthday.
The class Student is defined as a specialization of Person with +two additional properties, namely matnr and oncampus. The property +matnr is required (it has to be provided, when an instance of this +class is created), and the property oncampus is boolean, and is per +default set to true. Note that the class Student inherits the +properties of Person, therefore it will have 4 properties in total.
The property definitions are also used for providing object +parameters. These are non-positional parameters provided during +object creation to supply values to the instance variables. In our +listing, we create an instance of Person using the object parameter +name and provide the value of Bob to the instance variable name. +Similarly, we create an instance of Student using the two object +parameters name and matnr. Finally we use the accessor method +name to obtain the value of the instance variable name of object +s1.
+
+
+
+
+
+
+3.1.2. Instance Variables without Accessors
+In some cases one would like to define instance variables without +accessors, e.g. for keeping the internal state of an object. For this +purpose, one can use the predefined method variable, which is in +many respects similar to property. One difference is, that +property uses the same syntax as for method parameters, and +variable receives the default value as a separate argument (similar +to the variable command in Tcl. The introductory Stack example in in +Listing 2 used already the method +variable.
Listing 18: Declaring Variables
+
+
+
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + | Class create Base { + :variable x 1 + # ... +} + +Class create Derived -superclass Base { + :variable y 2 + # ... +} + +# Create instance of the class Derived +Derived create d1 + +# Object d1 has instance variables +# x == 1 and y == 2 |
Note that the variable definitions are inherited in the same way as +properties. The example in Listing 18 shows a +class Derived that inherits from Base. When an instance d1 is +created, it will contain the two instance variables x and y.
Listing 19: Setting Variables in the Constructor
+
+
+
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + | Class create Base2 { + # ... + :method init {} { + set :x 1 + # .... + } +} + +Class create Derived2 -superclass Base2 { + # ... + :method init {} { + set :y 2 + next + # .... + } +} + +# Create instance of the class Derived2 +Derived2 create d2 |
In many other object oriented languages, the instance variables are +initialized solely by the constructor, similar to class Derived2 in +Listing 19 . This approach is certainly as +well possible in NX. Note however, that the approach using +constructors requires an explicit method chaining between the +constructors and is less declarative.
+
+3.2. Method Definitions
+
+
+3.2.1. Scripted Methods
+
+
+3.2.2. C-implemented Methods
+
+
+3.2.3. Method-Aliases
+
+
+3.3. Method Protection
+
+
+3.4. Scopes of Methods
+
+
+3.4.1. Inherited Methods
+
+
+3.4.2. Class Methods
+
+
+3.4.3. Object Methods
+
+
+methods (we refer to these as method parameters) or to objects
+(these are called object parameters). Both kind of parameters
+might have different features, such as:
3.5. Parameters
NX provides a generalized mechanism for passing values to either -methods or to objects as initializers.
-
@@ -1540,15 +1855,21 @@
TODO: complete list above and provide a short summary of the section
Before we discuss method and object parameters in more detail, we +describe the parameter features in the subsequent sections based on +method parameters.
-
-
+
+
-
-
-
-
-
-
-
-
-
-3.1.1. Positional and Non-Positional Parameters
-In general, we distinguish between positional and non-positional -parameters. When we call a method with positional parameters, the -meaning of the parameters (the association with the argument in the -argument list of the method) is determined by its position. When we -call a method with non-positional parameters, their meaning is -determined via a name passed with the argument during invocation.
Listing 16: Positional and Non-Positional Method Parameters
3.5.1. Positional and Non-Positional Parameters
+If the position of a parameter in the list of formal arguments +(e.g. passed to a function) is significant for its meaning, this is a +positional parameter. If the meaning of the parameter is independent +of its postion, this is a non-positional parameter. When we call a +method with positional parameters, the meaning of the parameters (the +association with the argument in the argument list of the method) is +determined by its position. When we call a method with non-positional +parameters, their meaning is determined via a name passed with the +argument during invocation.
Listing 20: Positional and Non-Positional Method Parameters
-
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - | 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 - } -} |
Listing 28 shows a method foo -of some class C referring to differently scoped variables.
So, in general, there is no need to define or declare instance -variables in NX. However, in some cases, a definition is useful. For -example, one can define properties on classes, which are inherited to -subclasses, and which are used during object initialization. As shown -in the example class Student, properties can have defaults, which -are used as well during initialization.
In short, a property is an instance variable with accessors, where -the property definition might carry as well value-constraints and a -default value.
In some cases one would like to define instance variables without -accessors, e.g. for keeping the internal state of an object. For this -purpose, one can use the predefined method variable, which is in -many respects similar to property. One difference is, that -property uses the same syntax as for method parameters, and -variable receives the default value as a separate argument (similar -to the variable command in Tcl. The introductory Stack example in in -Listing 2 used already the method -variable.
Listing 29: Declaring Variables
-
-
-
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - | Class create Base { - :variable x 1 - # ... -} - -Class create Derived -superclass Base { - :variable y 2 - # ... -} - -# Create instance of the class Derived -Derived create d1 - -# Object d1 has instance variables -# x == 1 and y == 2 |
Note that the variable definitions are inherited in the same way as -properties. The example in Listing 29 shows a -class Derived that inherits from Base. When an instance d1 is -created, it will contain the two instance variables x and y.
Listing 30: Setting Variables in the Constructor
-
-
-
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - | Class create Base2 { - # ... - :method init {} { - set :x 1 - # .... - } -} - -Class create Derived2 -superclass Base2 { - # ... - :method init {} { - set :y 2 - next - # .... - } -} - -# Create instance of the class Derived2 -Derived2 create d2 |
In many other object oriented languages, the instance variables are -initialized by the constructor, similar to class Derived2 in -Listing 30 . This approach is certainly -as well possible in NX. Note however, that the approach using -constructors requires an explicit method chaining between the -constructors and is less declarative.
-
3.2.4. Additional Parameter Types for Object Parameters
+4.2.3. User defined Parameter Types
More detailed definition of the object parameter types comes here.
-
-
3.2.5. Slot Classes and Slot Objects
+4.2.4. Slot Classes and Slot Objects
In one of the previous sections, we defined scripted (application defined) checker methods on a class named nx::Slot. In general NX offers the possibility to define value checkers not only for all @@ -2640,12 +2783,12 @@
Figure 31. Slot Classes and Objects
+Figure 32. Slot Classes and Objects
-
3.2.6. Attribute Slots
+4.2.5. Attribute Slots
Still Missing
- @@ -2684,15 +2827,13 @@
-
-4. Method Protection
-
-
-5. Miscellaneous
-
+5.1. Unknown Handlers
+5.1. Profiling
+
+
5.2. Unknown Handlers
NX provides two kinds of unknown handlers:
- @@ -2707,12 +2848,12 @@
-
-
+
5.1.1. Unknown Handlers for Methods
+5.2.1. Unknown Handlers for Methods
Object and classes might be equipped with a method unknown which is called in cases, where an unknown method is called. The method unknown receives as first argument the called method followed by the provided arguments
Listing 32: Unknown Method Handler
Listing 33: Unknown Method Handler