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<body class="article">
<div id="header">
<h1>Listing of doc/example-scripts/starmethod.tcl</h1>
</div>
<div id="content">
<h1 id="_star_methods">Star Methods</h1>
<div class="paragraph"><p>Design study for implementing methods which applies to instances of
instances meta-classes. This study implements in addition to the
regular "method" a new construct called "*method" which has the
mentioned transitive property. The same behavior can be achieved in
many ways. In this study, we define a special class (the method
container class for *methods) which is kept in the precedence path
of instances. This way, it can be defined freely with other
extension mechanisms such as mixins, traits or filters.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
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table.nx        {border-collapse: collapse; border-spacing: 3px;}
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<pre class='nx'><span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>eval</span> {
    <span class='nx-comment'>#
</span>    <span class='nx-comment'># Define a *method, which is a method that applies for instances of
</span>    <span class='nx-comment'># the instances of a meta-class.
</span>    <span class='nx-comment'># - *methods are only defineable on meta-classes
</span>    <span class='nx-comment'># - *methods are applicable on the instances of the instances of the
</span>    <span class='nx-comment'>#   meta-class
</span>    <span class='nx-comment'># - If one defines a *method "bar" on a meta-class "MClass", and a
</span>    <span class='nx-comment'>#   class "C" as an instance of "MClass", and "c1" is an instance of
</span>    <span class='nx-comment'>#   "C", then "bar" is applicable for "c1".
</span>
    <span class='nx-comment'>#
</span>    <span class='nx-comment'># The "*method" has the same signature as regular methods, and can
</span>    <span class='nx-comment'># be used in combination with the modifiers
</span>    <span class='nx-comment'># public/protected/private as usual.
</span>    <span class='nx-comment'>#
</span>    <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> *<span class='nx-keyword'>method</span> {name arguments:parameter,0..* -returns body -precondition -postcondition} {
        <span class='nx-comment'>#
</span>        <span class='nx-comment'># Allow the definition only on meta-classes
</span>        <span class='nx-comment'>#
</span>        <span class='nx-keyword'>if</span> {![nsf::is <span class='nx-keyword'>metaclass</span> [<span class='nx-keyword'>self</span>]]} {
            <span class='nx-keyword'>error</span> <span class='nx-string'>"[self] is not a meta-class"</span>
        }
        <span class='nx-comment'>#
</span>        <span class='nx-comment'># Do we have the class for keeping the *methods already?
</span>        <span class='nx-comment'>#
</span>        <span class='nx-keyword'>set</span> starClass [<span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> [<span class='nx-keyword'>self</span>]::*]

        <span class='nx-keyword'>if</span> {![nsf::object::exists <span class='nx-variable'>$starClass</span>]} {
            <span class='nx-comment'>#
</span>            <span class='nx-comment'># If not, create the *method container class and provide
</span>            <span class='nx-comment'># it as a default in the superclass hierarchy. This
</span>            <span class='nx-comment'># happens by modifying the property "-superclasses" which
</span>            <span class='nx-comment'># is used on every class to specify the class hierarchy.
</span>            <span class='nx-comment'>#
</span>            <span class='nx-keyword'>:property</span> [<span class='nx-keyword'>list</span> superclasses <span class='nx-variable'>$starClass</span>] {
                <span class='nx-comment'>#
</span>                <span class='nx-comment'># Define a slot-specific method for keeping the
</span>                <span class='nx-comment'># *method container class in the hierarchy.
</span>                <span class='nx-comment'>#
</span>                <span class='nx-keyword'>:public</span> <span class='nx-keyword'>object</span> <span class='nx-keyword'>method</span> appendToRelations { <span class='nx-keyword'>class</span> <span class='nx-keyword'>property</span> value } {
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                    }
                }

                <span class='nx-comment'>#
</span>                <span class='nx-comment'># Whenever the "-superclasses" relation is called,
</span>                <span class='nx-comment'># make sure, we keep the *method container class in
</span>                <span class='nx-comment'># the hierarchy.
</span>                <span class='nx-comment'>#
</span>                <span class='nx-keyword'>:public</span> <span class='nx-keyword'>object</span> <span class='nx-keyword'>method</span> value=<span class='nx-keyword'>set</span> { <span class='nx-keyword'>class</span> <span class='nx-keyword'>property</span> value } {
                    :appendToRelations <span class='nx-variable'>$class</span> <span class='nx-keyword'>superclass</span> <span class='nx-variable'>$value</span>
                }
            }

            <span class='nx-comment'>#
</span>            <span class='nx-comment'># Update class hierarchies of the previously created instances
</span>            <span class='nx-comment'># of the meta-class.
</span>            <span class='nx-comment'>#
</span>            <span class='nx-keyword'>foreach</span> <span class='nx-keyword'>class</span> [<span class='nx-keyword'>:info</span> instances] {
                <span class='nx-keyword'>set</span> slot [<span class='nx-variable'>$class</span> <span class='nx-keyword'>info</span> <span class='nx-keyword'>lookup</span> slots superclasses]
                <span class='nx-variable'>$slot</span> appendToRelations <span class='nx-variable'>$class</span> <span class='nx-keyword'>superclass</span> <span class='nx-variable'>$starClass</span>
            }
        }

        <span class='nx-comment'>#
</span>        <span class='nx-comment'># Define the *method as regular method in the star method
</span>        <span class='nx-comment'># container class.
</span>        <span class='nx-comment'>#
</span>        [<span class='nx-keyword'>self</span>]::* <span class='nx-keyword'>method</span> <span class='nx-variable'>$name</span> <span class='nx-variable'>$arguments</span> \
            {*}[<span class='nx-keyword'>expr</span> {[<span class='nx-keyword'>info</span> exists returns] ? [<span class='nx-keyword'>list</span> -returns <span class='nx-variable'>$returns</span>] : <span class='nx-string'>""</span>}] \
            <span class='nx-variable'>$body</span> \
            {*}[<span class='nx-keyword'>expr</span> {[<span class='nx-keyword'>info</span> exists precondition]  ? [<span class='nx-keyword'>list</span> -precondition <span class='nx-variable'>$precondition</span>] : <span class='nx-string'>""</span>}] \
            {*}[<span class='nx-keyword'>expr</span> {[<span class='nx-keyword'>info</span> exists postcondition] ? [<span class='nx-keyword'>list</span> -postcondition <span class='nx-variable'>$postcondition</span>] : <span class='nx-string'>""</span>}]
    }
}
<span class='nx-keyword'>set</span> ::nsf::methodDefiningMethod(*<span class='nx-keyword'>method</span>) 1</pre></div></div>
<div class="sect1">
<h2 id="_some_base_test_cases">Some base test cases:</h2>
<div class="sectionbody">
<div class="paragraph"><p>Define a meta-class MClass with a method "foo" and to star methods
named "foo" and "bar".</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'><span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> MClass -superclass <span class='nx-keyword'>nx::Class</span> {
    <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> foo {} {<span class='nx-keyword'>return</span> MClass-[<span class='nx-keyword'>next</span>]}
    <span class='nx-keyword'>:public</span> *<span class='nx-keyword'>method</span> foo {} {<span class='nx-keyword'>return</span> *-[<span class='nx-keyword'>next</span>]}
    <span class='nx-keyword'>:public</span> *<span class='nx-keyword'>method</span> bar {} {<span class='nx-keyword'>return</span> *-[<span class='nx-keyword'>next</span>]}
}</pre></div></div>
<div class="paragraph"><p>Define a class based on MClass and define here as well a method
"foo" to show the next-path in combination with the *methods.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>MClass <span class='nx-keyword'>create</span> C {
    <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> foo {} {<span class='nx-keyword'>return</span> C-[<span class='nx-keyword'>next</span>]}
}

% C <span class='nx-keyword'>info</span> superclasses
::MClass::*</pre></div></div>
<div class="paragraph"><p>Finally create an instance with the method foo as well.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>C <span class='nx-keyword'>create</span> c1 {
    <span class='nx-keyword'>:public</span> <span class='nx-keyword'>object</span> <span class='nx-keyword'>method</span> foo {} {<span class='nx-keyword'>return</span> c1-[<span class='nx-keyword'>next</span>]}
}</pre></div></div>
<div class="paragraph"><p>The result of "foo" reflects the execution order: object before
classes (including the *method container).</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% c1 <span class='nx-keyword'>info</span> precedence
::C ::MClass::* ::nx::Object
% c1 foo
c1-C-*-
% c1 bar
*-</pre></div></div>
<div class="paragraph"><p>Define a Class D as a specialization of C</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>MClass <span class='nx-keyword'>create</span> D -superclass C {
    <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> foo {} {<span class='nx-keyword'>return</span> D-[<span class='nx-keyword'>next</span>]}
    <span class='nx-keyword'>:create</span> d1
}

% d1 <span class='nx-keyword'>info</span> precedence
::D ::C ::MClass::* ::nx::Object
% d1 foo
D-C-*-</pre></div></div>
<div class="paragraph"><p>Dynamically add *method "baz".</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% d1 baz
::d1: unable to <span class='nx-keyword'>dispatch</span> <span class='nx-keyword'>method</span> 'baz'
MClass <span class='nx-keyword'>eval</span> {
    <span class='nx-keyword'>:public</span> *<span class='nx-keyword'>method</span> baz {} {<span class='nx-keyword'>return</span> baz*-[<span class='nx-keyword'>next</span>]}
}
% d1 baz
baz*-</pre></div></div>
<div class="paragraph"><p>Test adding of *methods at a time, when the meta-class has already
instances.</p></div>
<div class="paragraph"><p>Create a meta-class without a *method</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'><span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> MClass2 -superclass <span class='nx-keyword'>nx::Class</span>
MClass2 <span class='nx-keyword'>create</span> X {<span class='nx-keyword'>:create</span> x1}
% x1 <span class='nx-keyword'>info</span> precedence
::X ::nx::Object</pre></div></div>
<div class="paragraph"><p>Now add a *method</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>MClass2 <span class='nx-keyword'>eval</span> {
    <span class='nx-keyword'>:public</span> *<span class='nx-keyword'>method</span> baz {} {<span class='nx-keyword'>return</span> baz*-[<span class='nx-keyword'>next</span>]}
}</pre></div></div>
<div class="paragraph"><p>Adding the *method alters the superclass order of already created
instances of the meta-class</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% x1 <span class='nx-keyword'>info</span> precedence
::X ::MClass2::* ::nx::Object
% x1 baz
baz*-</pre></div></div>
<div class="paragraph"><p>Finally, there is a simple application example for ActiveRecord
pattern. All instances of the application classes (such as
"Product") should have a method "save" (together with other methods
now shown here). First define the ActiveRecord class (as a
meta-class).</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'><span class='nx-keyword'>Class</span> <span class='nx-keyword'>create</span> ActiveRecord -superclass <span class='nx-keyword'>nx::Class</span> {
    <span class='nx-keyword'>:property</span> table_name

    <span class='nx-keyword'>:method</span> <span class='nx-keyword'>init</span> {} {
        <span class='nx-keyword'>if</span> {![<span class='nx-keyword'>info</span> exists :table_name]} {
            <span class='nx-keyword'>set</span> :table_name [<span class='nx-keyword'>string</span> tolower [<span class='nx-keyword'>namespace</span> tail [<span class='nx-keyword'>self</span>]]s]
        }
    }
    <span class='nx-keyword'>:public</span> *<span class='nx-keyword'>method</span> save {} {
        <span class='nx-keyword'>puts</span> <span class='nx-string'>"save [self] into table [[:info class] cget -table_name]"</span>
    }
}</pre></div></div>
<div class="paragraph"><p>Define the application class "Product" with an instance</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>ActiveRecord <span class='nx-keyword'>create</span> Product
Product <span class='nx-keyword'>create</span> p1
p1 save</pre></div></div>
<div class="paragraph"><p>The last command prints out: "save ::p1 into table products"</p></div>
</div>
</div>
</div>
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Last updated 2018-07-02 12:14:21 CEST
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