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<body class="article">
<div id="header">
<h1>Listing of doc/example-scripts/ruby-mixins.tcl</h1>
</div>
<div id="content">
<div class="sect1">
<h2 id="_design_study_to_show_the_differences_between_decorator_mixin_classes_and_ruby_8217_s_mixin_modules">Design study to show the differences between decorator mixin classes and Ruby’s mixin modules</h2>
<div class="sectionbody">
<div class="paragraph"><p>This example shows that the dynamic class structure of NX (and
XOTcl) is able to support <em>Ruby style mixins</em> (called modules) and
<em>decorator style mixins</em> (named after the design pattern Decorator)
in the same script.</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'>nx::test <span class='nx-keyword'>configure</span> -count 1</pre></div></div>
<div class="paragraph"><p>One important difference between mixin classes in NX and Ruby’s
mixins is the precedence order. While in NX, mixins are decorators
(the mixins have higher precedence than the intrinsic classes,
therefore a mixin class can overload the methods of the current
class and its subclasses), the mixins of Ruby have a lower
precedence (they extend the <em>base behavior</em>; although Ruby’s modules
are not full classes, they are folded into the <em>intrinsic class
hierarchy</em>). Therefore, a Ruby style mixin can be refined by the
class, into which it is mixed in (or by a subclass). Decorator style
mixins modify the behavior of a full intrinsic class tree, while
Ruby style mixins are compositional units for a single class.</p></div>
<div class="paragraph"><p>To show the differences, we define the method <code>module</code>, which
behaves somewhat similar to Ruby’s <code>module</code> command. This method
adds the provided class to the precedence order after the current
class. The easiest way to achieve this is via multiple inheritance
(i.e. via the <code>superclass</code> relationship).</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
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</style>
<pre class='nx'><span class='nx-keyword'>package</span> req nx
<span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>eval</span> {
<span class='nx-keyword'>:protected</span> <span class='nx-keyword'>method</span> module {name<span class='nx-keyword'>:class</span>} {
nsf::relation [<span class='nx-keyword'>self</span>] <span class='nx-keyword'>superclass</span> [<span class='nx-keyword'>concat</span> <span class='nx-variable'>$name</span> [<span class='nx-keyword'>:info</span> <span class='nx-keyword'>superclass</span>]]
}
}</pre></div></div>
<div class="paragraph"><p>For illustration of the behavior of <code>module</code> we define a class
<code>Enumerable</code> somewhat inspired by the Ruby module with the same
name. We define here just the methods <code>map</code>, <code>each</code>, <code>count</code>, and
<code>count_if</code>.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
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.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'><span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> Enumerable {
<span class='nx-keyword'>:property</span> members:0..n
<span class='nx-comment'># The method 'each' applies the provided block on every element of
</span> <span class='nx-comment'># 'members'
</span> <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> each {var block} {
<span class='nx-keyword'>foreach</span> member <span class='nx-variable'>${</span><span class='nx-variable'>:members}</span> {
<span class='nx-keyword'>uplevel</span> [<span class='nx-keyword'>list</span> <span class='nx-keyword'>set</span> <span class='nx-variable'>$var</span> <span class='nx-variable'>$member</span>]
<span class='nx-keyword'>uplevel</span> <span class='nx-variable'>$block</span>
}
}
<span class='nx-comment'># The method 'map' applies the provided block on every element of
</span> <span class='nx-comment'># 'members' and returns a list, where every element is the mapped
</span> <span class='nx-comment'># result of the source.
</span> <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> map {var block} {
<span class='nx-keyword'>set</span> result [<span class='nx-keyword'>list</span>]
:each <span class='nx-variable'>$var</span> {
<span class='nx-keyword'>uplevel</span> [<span class='nx-keyword'>list</span> <span class='nx-keyword'>set</span> <span class='nx-variable'>$var</span> [<span class='nx-keyword'>set</span> <span class='nx-variable'>$var</span>]]
<span class='nx-keyword'>lappend</span> result [<span class='nx-keyword'>uplevel</span> <span class='nx-variable'>$block</span>]
}
<span class='nx-keyword'>return</span> <span class='nx-variable'>$result</span>
}
<span class='nx-comment'># The method 'count' returns the number of elements.
</span> <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> count {} {
<span class='nx-keyword'>return</span> [<span class='nx-keyword'>llength</span> <span class='nx-variable'>${</span><span class='nx-variable'>:members}</span>]
}
<span class='nx-comment'># The method 'count_if' returns the number of elements for which
</span> <span class='nx-comment'># the provided expression is true.
</span> <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> count_if {var <span class='nx-keyword'>expr</span>} {
<span class='nx-keyword'>set</span> result 0
:each <span class='nx-variable'>$var</span> {
<span class='nx-keyword'>incr</span> result [<span class='nx-keyword'>expr</span> <span class='nx-variable'>$expr</span>]
}
<span class='nx-keyword'>return</span> <span class='nx-variable'>$result</span>
}
}</pre></div></div>
<div class="paragraph"><p>After having defined the class <code>Enumerable</code>, we define a class
<code>Group</code> using <code>Enumerable</code> as a Ruby style mixin. This makes
essentially <code>Group</code> a subclass of <code>Enumerable</code>, but with the only
difference that <code>Group</code> might have other superclasses 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'><span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> Group {
<span class='nx-comment'>#
</span> <span class='nx-comment'># Include the "module" Enumerable
</span> <span class='nx-comment'>#
</span> :module Enumerable
}</pre></div></div>
<div class="paragraph"><p>Define now a group <code>g1</code> with the three provided members.</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'>% Group <span class='nx-keyword'>create</span> g1 -members {mini trix trax}
::g1</pre></div></div>
<div class="paragraph"><p>Since the definition of <code>Group</code> includes the module <code>Enumerable</code>,
this class is listed in the precedence order after the class <code>Group</code>:</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'>% g1 <span class='nx-keyword'>info</span> precedence
::Group ::Enumerable ::nx::Object</pre></div></div>
<div class="paragraph"><p>Certainly, we can call the methods of <code>Enumerable</code> as usual:</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'>% g1 count
3
% g1 map x {<span class='nx-keyword'>list</span> pre-<span class='nx-variable'>$x</span>-post}
pre-mini-post pre-trix-post pre-trax-post
% g1 count_if x {[<span class='nx-keyword'>string</span> match tr*x <span class='nx-variable'>$x</span>] > 0}
2</pre></div></div>
<div class="paragraph"><p>To show the difference between a <code>module</code> and a <code>decorator mixin</code> we
define a class named <code>Mix</code> with the single method <code>count</code>, which
wraps the result of the underlaying <code>count</code> method between the
<code>alpha</code> and <code>omega</code>.</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> Mix {
<span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> count {} {
<span class='nx-keyword'>return</span> [<span class='nx-keyword'>list</span> alpha [<span class='nx-keyword'>next</span>] omega]
}
}</pre></div></div>
<div class="paragraph"><p>When the mixin class is added to <code>g1</code>, it is added to the front of
the precedence list. A decorator is able to modify the behavior of
all of the methods of the class, where it is mixed into.</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'>% g1 <span class='nx-keyword'>object</span> <span class='nx-keyword'>mixin</span> Mix
::Mix
% g1 <span class='nx-keyword'>info</span> precedence
::Mix ::Group ::Enumerable ::nx::Object
% g1 count
alpha 3 omega</pre></div></div>
<div class="paragraph"><p>For the time being, remove the mixin class again.</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'>% g1 <span class='nx-keyword'>object</span> <span class='nx-keyword'>mixin</span> <span class='nx-string'>""</span>
% g1 <span class='nx-keyword'>info</span> precedence
::Group ::Enumerable ::nx::Object</pre></div></div>
<div class="paragraph"><p>An important difference between NX/XOTcl style mixins (decorators)
and Ruby style modules is that the decorator will have always a
higher precedence than the intrinsic classes, while the <code>module</code> is
folded into the precedence path.</p></div>
<div class="paragraph"><p>Define a class <code>ATeam</code> that uses <code>Enumerable</code> in the style of a Ruby
module. The class might refine some of the provided methods. We
refined the method <code>each</code>, which is used as well by the other
methods. In general, by defining <code>each</code> one can define very
different kind of enumerators (for lists, databases, etc.).</p></div>
<div class="paragraph"><p>Since <code>Enumerable</code> is a module, the definition of <code>each</code> in the
class <code>ATeam</code> has a higher precedence than the definition in the
class <code>Enumerable</code>. If <code>Enumerable</code> would be a decorator style mixin
class, it would not e possible to refine the definition in the class
<code>ATeam</code>, but maybe via another 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'><span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> ATeam {
<span class='nx-comment'>#
</span> <span class='nx-comment'># Include the "module" Enumerable
</span> <span class='nx-comment'>#
</span> :module Enumerable
<span class='nx-comment'>#
</span> <span class='nx-comment'># Overload "each"
</span> <span class='nx-comment'>#
</span> <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> each {var block} {
<span class='nx-keyword'>foreach</span> member <span class='nx-variable'>${</span><span class='nx-variable'>:members}</span> {
<span class='nx-keyword'>uplevel</span> [<span class='nx-keyword'>list</span> <span class='nx-keyword'>set</span> <span class='nx-variable'>$var</span> <span class='nx-variable'>$member</span>-[<span class='nx-keyword'>string</span> length <span class='nx-variable'>$member</span>]]
<span class='nx-keyword'>uplevel</span> <span class='nx-variable'>$block</span>
}
}
<span class='nx-comment'>#
</span> <span class='nx-comment'># Use "map", which uses the "each" method defined in this class.
</span> <span class='nx-comment'>#
</span> <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> foo {} {
<span class='nx-keyword'>return</span> [:map x {<span class='nx-keyword'>string</span> totitle <span class='nx-variable'>$x</span>}]
}
}</pre></div></div>
<div class="paragraph"><p>Define now a team <code>t1</code> with the three provided members.</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'>% ATeam <span class='nx-keyword'>create</span> t1 -members {arthur bill chuck}
::t1</pre></div></div>
<div class="paragraph"><p>As above, the precedence of <code>ATeam</code> is higher than the precedence of
<code>Enumerable</code>. Therefore, the object <code>t1</code> uses the method <code>each</code> specialized in
class <code>ATeam</code>:</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'>% t1 <span class='nx-keyword'>info</span> precedence
::ATeam ::Enumerable ::nx::Object
% t1 foo
Arthur-6 Bill-4 Chuck-5</pre></div></div>
<div class="paragraph"><p>The class <code>ATeam</code> can be specialized further by a class <code>SpecialForce</code>:</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> SpecialForce -superclass ATeam {
<span class='nx-comment'># ...
</span>}</pre></div></div>
<div class="paragraph"><p>Define a special force <code>s1</code> with the four provided members.</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'>% SpecialForce <span class='nx-keyword'>create</span> s1 -members {Donald Micky Daniel Gustav}
::s1</pre></div></div>
<div class="paragraph"><p>As above, the precedence of <code>Enumerable</code> is lower then the
precedence of <code>ATeam</code> and <code>Enumerable</code>. Therefore <code>ATeam</code> can refine
the behavior of <code>Enumerable</code>, the class <code>SpecialForce</code> can refine
the behavior of <code>ATeam</code>.</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'>% s1 <span class='nx-keyword'>info</span> precedence
::SpecialForce ::ATeam ::Enumerable ::nx::Object
% s1 foo
Donald-6 Micky-5 Daniel-6 Gustav-6</pre></div></div>
<div class="paragraph"><p>Let us look again on decorator style mixin classes. If we add a
per-class mixin to <code>ATeam</code>, the mixin class has highest precedence,
and decorates the instances of <code>ATeam</code> as well the instances of its
specializations (like e.g. <code>SpecialForce</code>).</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'>% ATeam <span class='nx-keyword'>mixin</span> Mix
::Mix
% s1 <span class='nx-keyword'>info</span> precedence
::Mix ::SpecialForce ::ATeam ::Enumerable ::nx::Object
% s1 count
alpha 4 omega</pre></div></div>
<div class="paragraph"><p>This example showed that NX/XOTcl dynamic class structure is able to
support Ruby-style mixins, and decorator style mixins in the same script.</p></div>
</div>
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Last updated 2013-06-07 00:16:54 CEST
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