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<body class="article">
<div id="header">
<h1>Listing of doc/example-scripts/per-object-mixins.tcl</h1>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p>NX supports "open class definitions", object specific behavior
and mixin classes (among other things) to achieve dynamic behavior
extensions. The so-called per-object mixins are actually an
implementation of the decorator pattern.</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'>package</span> req nx</pre></div></div>
<div class="paragraph"><p>Here is the original example: a method from a derived class
extends the behavior of the baseclass; the primitive "next"
calls other same-named methods. In the example below, the
baseclass method "speak" is called at the beginning of the
derived-class method. The primitive "next" can be placed at
arbitrary places, or it can be omitted when the baseclass method
should not be called.</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> BaseClass {
:<span class='nx-keyword'>public</span> <span class='nx-keyword'>method</span> speak {} {
<span class='nx-keyword'>puts</span> <span class='nx-string'>"Hello from BC."</span>
}
}
<span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> DerivedClass -<span class='nx-keyword'>superclass</span> BaseClass {
:<span class='nx-keyword'>public</span> <span class='nx-keyword'>method</span> speak {} {
<span class='nx-keyword'>next</span>
<span class='nx-keyword'>puts</span> <span class='nx-string'>"Hello from DC."</span>
}
}
DerivedClass <span class='nx-keyword'>create</span> o1
o1 speak</pre></div></div>
<div class="paragraph"><p>The output is:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt> Hello from BC.
Hello from DC.</tt></pre>
</div></div>
<div class="paragraph"><p>There are many ways to extend the behavior NX classes at
runtime. The easiest thing is to add methods dynamically to
classes. E.g. we can extend the BaseClass with the method unknown,
which is called whenever an unknown method is called.</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;}
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.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'>BaseClass <span class='nx-keyword'>method</span> unknown {m args} {
<span class='nx-keyword'>puts</span> <span class='nx-string'>"What? $m? I don't understand."</span>
}
o1 sing</pre></div></div>
<div class="paragraph"><p>The output is:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt> What? sing? I don't understand.</tt></pre>
</div></div>
<div class="paragraph"><p>Often, you do not want to extend the class, but to
modify the behavior of a single object. In NX, an object
can have individual 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'>o1 <span class='nx-keyword'>public</span> <span class='nx-keyword'>method</span> sing {} {
<span class='nx-keyword'>puts</span> <span class='nx-string'>"Ok, here it goes: Lala Lala!"</span>
}
o1 sing</pre></div></div>
<div class="paragraph"><p>The output is:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt> Ok, here it goes: Lala Lala!</tt></pre>
</div></div>
<div class="paragraph"><p>In many situations, it is desired to add/remove a set
of methods dynamically to objects or classes. The mechanisms
above allow this, but they are rather cumbersome and do
support a systematic behavior engineering. One can add
so-called "mixin classes" to objects and/or classes. For
example, we can define a class M for a more verbose 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;}
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.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> M {
:<span class='nx-keyword'>public</span> <span class='nx-keyword'>method</span> sing {} {
<span class='nx-keyword'>puts</span> -nonewline <span class='nx-string'>"[self] sings: "</span>
<span class='nx-keyword'>next</span>
}
:<span class='nx-keyword'>method</span> unknown args {
<span class='nx-keyword'>puts</span> -nonewline <span class='nx-string'>"[self] is confused: "</span>
<span class='nx-keyword'>next</span>
}
}</pre></div></div>
<div class="paragraph"><p>The behavior of M can be mixed into the behavior of o1 through
per object mixins …</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'>o1 <span class='nx-keyword'>mixin</span> M</pre></div></div>
<div class="olist lowerroman"><ol class="lowerroman">
<li>
<p>
and we call the methods again:
</p>
</li>
</ol></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'>o1 sing
o1 <span class='nx-keyword'>read</span></pre></div></div>
<div class="paragraph"><p>The output is:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt> ::o1 sings: Ok, here it goes: Lala Lala!
::o1 is confused: What? read? I don't understand.</tt></pre>
</div></div>
<div class="paragraph"><p>We can remove the new behavior easily by unregistering the
mixin 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'>o1 <span class='nx-keyword'>mixin</span> <span class='nx-string'>""</span></pre></div></div>
<div class="olist lowerroman"><ol class="lowerroman">
<li>
<p>
and we call the methods again:
</p>
</li>
</ol></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'>o1 sing
o1 <span class='nx-keyword'>read</span></pre></div></div>
<div class="paragraph"><p>The output is:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt> Ok, here it goes: Lala Lala!
What? read? I don't understand.</tt></pre>
</div></div>
<div class="paragraph"><p>Mixin classes can be used to extend the behavior of classes
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'>BaseClass <span class='nx-keyword'>mixin</span> M
o1 sing
o1 <span class='nx-keyword'>read</span>
DerivedClass <span class='nx-keyword'>create</span> o2
o2 <span class='nx-keyword'>read</span></pre></div></div>
<div class="paragraph"><p>The output is:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt> ::o1 sings: Ok, here it goes: Lala Lala!
::o1 is confused: What? read? I don't understand.
::o2 is confused: What? read? I don't understand.</tt></pre>
</div></div>
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Last updated 2011-09-19 03:46:57 CEST
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