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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'> .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'>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 } { <span class='nx-keyword'>set</span> sc [nsf::relation::get <span class='nx-variable'>$class</span> <span class='nx-variable'>$property</span>] <span class='nx-keyword'>if</span> {<span class='nx-variable'>$sc</span> eq <span class='nx-string'>"::nx::Object"</span>} { nsf::relation::set <span class='nx-variable'>$class</span> <span class='nx-variable'>$property</span> <span class='nx-variable'>$value</span> } <span class='nx-keyword'>else</span> { nsf::relation::set <span class='nx-variable'>$class</span> <span class='nx-variable'>$property</span> [<span class='nx-keyword'>concat</span> <span class='nx-variable'>$sc</span> <span class='nx-variable'>$value</span>] } } <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> <div id="footnotes"><hr /></div> <div id="footer"> <div id="footer-text"> Last updated 2018-07-02 12:14:21 CEST </div> </div> </body> </html>