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<h3>Table of Contents</h3>
<ul class="link-list" role="directory">
<li><a href="#module-Forwardable-label-Another+example">Another example</a>
<li><a href="#module-Forwardable-label-Notes">Notes</a>
</ul>
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<!-- Method Quickref -->
<div id="method-list-section" class="nav-section">
<h3>Methods</h3>
<ul class="link-list" role="directory">
<li ><a href="#method-i-def_delegator">#def_delegator</a>
<li ><a href="#method-i-def_delegators">#def_delegators</a>
<li ><a href="#method-i-def_instance_delegator">#def_instance_delegator</a>
<li ><a href="#method-i-def_instance_delegators">#def_instance_delegators</a>
<li ><a href="#method-i-delegate">#delegate</a>
<li ><a href="#method-i-instance_delegate">#instance_delegate</a>
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<h1 id="module-Forwardable" class="module">
module Forwardable
</h1>
<section class="description">
<p>The Forwardable module provides delegation of specified methods to a designated object, using the methods <a href="Forwardable.html#method-i-def_delegator"><code>def_delegator</code></a> and <a href="Forwardable.html#method-i-def_delegators"><code>def_delegators</code></a>.</p>
<p>For example, say you have a class RecordCollection which contains an array <code>@records</code>. You could provide the lookup method record_number(), which simply calls [] on the <code>@records</code> array, like this:</p>
<pre class="ruby"><span class="ruby-identifier">require</span> <span class="ruby-string">'forwardable'</span>
<span class="ruby-keyword">class</span> <span class="ruby-constant">RecordCollection</span>
<span class="ruby-identifier">attr_accessor</span> <span class="ruby-value">:records</span>
<span class="ruby-identifier">extend</span> <span class="ruby-constant">Forwardable</span>
<span class="ruby-identifier">def_delegator</span> <span class="ruby-value">:@records</span>, <span class="ruby-value">:[]</span>, <span class="ruby-value">:record_number</span>
<span class="ruby-keyword">end</span>
</pre>
<p>We can use the lookup method like so:</p>
<pre class="ruby"><span class="ruby-identifier">r</span> = <span class="ruby-constant">RecordCollection</span>.<span class="ruby-identifier">new</span>
<span class="ruby-identifier">r</span>.<span class="ruby-identifier">records</span> = [<span class="ruby-value">4</span>,<span class="ruby-value">5</span>,<span class="ruby-value">6</span>]
<span class="ruby-identifier">r</span>.<span class="ruby-identifier">record_number</span>(<span class="ruby-value">0</span>) <span class="ruby-comment"># => 4</span>
</pre>
<p>Further, if you wish to provide the methods size, <<, and map, all of which delegate to @records, this is how you can do it:</p>
<pre class="ruby"><span class="ruby-keyword">class</span> <span class="ruby-constant">RecordCollection</span> <span class="ruby-comment"># re-open RecordCollection class</span>
<span class="ruby-identifier">def_delegators</span> <span class="ruby-value">:@records</span>, <span class="ruby-value">:size</span>, <span class="ruby-value">:<<</span>, <span class="ruby-value">:map</span>
<span class="ruby-keyword">end</span>
<span class="ruby-identifier">r</span> = <span class="ruby-constant">RecordCollection</span>.<span class="ruby-identifier">new</span>
<span class="ruby-identifier">r</span>.<span class="ruby-identifier">records</span> = [<span class="ruby-value">1</span>,<span class="ruby-value">2</span>,<span class="ruby-value">3</span>]
<span class="ruby-identifier">r</span>.<span class="ruby-identifier">record_number</span>(<span class="ruby-value">0</span>) <span class="ruby-comment"># => 1</span>
<span class="ruby-identifier">r</span>.<span class="ruby-identifier">size</span> <span class="ruby-comment"># => 3</span>
<span class="ruby-identifier">r</span> <span class="ruby-operator"><<</span> <span class="ruby-value">4</span> <span class="ruby-comment"># => [1, 2, 3, 4]</span>
<span class="ruby-identifier">r</span>.<span class="ruby-identifier">map</span> { <span class="ruby-operator">|</span><span class="ruby-identifier">x</span><span class="ruby-operator">|</span> <span class="ruby-identifier">x</span> <span class="ruby-operator">*</span> <span class="ruby-value">2</span> } <span class="ruby-comment"># => [2, 4, 6, 8]</span>
</pre>
<p>You can even extend regular objects with Forwardable.</p>
<pre class="ruby"><span class="ruby-identifier">my_hash</span> = <span class="ruby-constant">Hash</span>.<span class="ruby-identifier">new</span>
<span class="ruby-identifier">my_hash</span>.<span class="ruby-identifier">extend</span> <span class="ruby-constant">Forwardable</span> <span class="ruby-comment"># prepare object for delegation</span>
<span class="ruby-identifier">my_hash</span>.<span class="ruby-identifier">def_delegator</span> <span class="ruby-string">"STDOUT"</span>, <span class="ruby-string">"puts"</span> <span class="ruby-comment"># add delegation for STDOUT.puts()</span>
<span class="ruby-identifier">my_hash</span>.<span class="ruby-identifier">puts</span> <span class="ruby-string">"Howdy!"</span>
</pre>
<h2 id="module-Forwardable-label-Another+example">Another example<span><a href="#module-Forwardable-label-Another+example">¶</a> <a href="#top">↑</a></span></h2>
<p>You could use Forwardable as an alternative to inheritance, when you don't want to inherit all methods from the superclass. For instance, here is how you might add a range of <code>Array</code> instance methods to a new class <code>Queue</code>:</p>
<pre class="ruby"><span class="ruby-keyword">class</span> <span class="ruby-constant">Queue</span>
<span class="ruby-identifier">extend</span> <span class="ruby-constant">Forwardable</span>
<span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">initialize</span>
<span class="ruby-ivar">@q</span> = [ ] <span class="ruby-comment"># prepare delegate object</span>
<span class="ruby-keyword">end</span>
<span class="ruby-comment"># setup preferred interface, enq() and deq()...</span>
<span class="ruby-identifier">def_delegator</span> <span class="ruby-value">:@q</span>, <span class="ruby-value">:push</span>, <span class="ruby-value">:enq</span>
<span class="ruby-identifier">def_delegator</span> <span class="ruby-value">:@q</span>, <span class="ruby-value">:shift</span>, <span class="ruby-value">:deq</span>
<span class="ruby-comment"># support some general Array methods that fit Queues well</span>
<span class="ruby-identifier">def_delegators</span> <span class="ruby-value">:@q</span>, <span class="ruby-value">:clear</span>, <span class="ruby-value">:first</span>, <span class="ruby-value">:push</span>, <span class="ruby-value">:shift</span>, <span class="ruby-value">:size</span>
<span class="ruby-keyword">end</span>
<span class="ruby-identifier">q</span> = <span class="ruby-constant">Queue</span>.<span class="ruby-identifier">new</span>
<span class="ruby-identifier">q</span>.<span class="ruby-identifier">enq</span> <span class="ruby-value">1</span>, <span class="ruby-value">2</span>, <span class="ruby-value">3</span>, <span class="ruby-value">4</span>, <span class="ruby-value">5</span>
<span class="ruby-identifier">q</span>.<span class="ruby-identifier">push</span> <span class="ruby-value">6</span>
<span class="ruby-identifier">q</span>.<span class="ruby-identifier">shift</span> <span class="ruby-comment"># => 1</span>
<span class="ruby-keyword">while</span> <span class="ruby-identifier">q</span>.<span class="ruby-identifier">size</span> <span class="ruby-operator">></span> <span class="ruby-value">0</span>
<span class="ruby-identifier">puts</span> <span class="ruby-identifier">q</span>.<span class="ruby-identifier">deq</span>
<span class="ruby-keyword">end</span>
<span class="ruby-identifier">q</span>.<span class="ruby-identifier">enq</span> <span class="ruby-string">"Ruby"</span>, <span class="ruby-string">"Perl"</span>, <span class="ruby-string">"Python"</span>
<span class="ruby-identifier">puts</span> <span class="ruby-identifier">q</span>.<span class="ruby-identifier">first</span>
<span class="ruby-identifier">q</span>.<span class="ruby-identifier">clear</span>
<span class="ruby-identifier">puts</span> <span class="ruby-identifier">q</span>.<span class="ruby-identifier">first</span>
</pre>
<p>This should output:</p>
<pre class="ruby"><span class="ruby-value">2</span>
<span class="ruby-value">3</span>
<span class="ruby-value">4</span>
<span class="ruby-value">5</span>
<span class="ruby-value">6</span>
<span class="ruby-constant">Ruby</span>
<span class="ruby-keyword">nil</span>
</pre>
<h2 id="module-Forwardable-label-Notes">Notes<span><a href="#module-Forwardable-label-Notes">¶</a> <a href="#top">↑</a></span></h2>
<p>Be advised, <a href="RDoc.html"><code>RDoc</code></a> will not detect delegated methods.</p>
<p><code>forwardable.rb</code> provides single-method delegation via the <a href="Forwardable.html#method-i-def_delegator"><code>def_delegator</code></a> and <a href="Forwardable.html#method-i-def_delegators"><code>def_delegators</code></a> methods. For full-class delegation via DelegateClass, see <code>delegate.rb</code>.</p>
</section>
<section id="5Buntitled-5D" class="documentation-section">
<section class="constants-list">
<header>
<h3>Constants</h3>
</header>
<dl>
<dt id="FORWARDABLE_VERSION">FORWARDABLE_VERSION
<dd>
<dt id="VERSION">VERSION
<dd><p>Version of <code>forwardable.rb</code></p>
</dl>
</section>
<section class="attribute-method-details" class="method-section">
<header>
<h3>Attributes</h3>
</header>
<div id="attribute-c-debug" class="method-detail">
<div class="method-heading attribute-method-heading">
<span class="method-name">debug</span><span
class="attribute-access-type">[RW]</span>
</div>
<div class="method-description">
<p>ignored</p>
</div>
</div>
</section>
<section id="public-instance-5Buntitled-5D-method-details" class="method-section">
<header>
<h3>Public Instance Methods</h3>
</header>
<div id="method-i-def_delegator" class="method-detail method-alias">
<div class="method-heading">
<span class="method-name">def_delegator</span><span
class="method-args">(accessor, method, ali = method)</span>
</div>
<div class="method-description">
</div>
<div class="aliases">
Alias for: <a href="Forwardable.html#method-i-def_instance_delegator">def_instance_delegator</a>
</div>
</div>
<div id="method-i-def_delegators" class="method-detail method-alias">
<div class="method-heading">
<span class="method-name">def_delegators</span><span
class="method-args">(accessor, *methods)</span>
</div>
<div class="method-description">
</div>
<div class="aliases">
Alias for: <a href="Forwardable.html#method-i-def_instance_delegators">def_instance_delegators</a>
</div>
</div>
<div id="method-i-def_instance_delegator" class="method-detail ">
<div class="method-heading">
<span class="method-name">def_instance_delegator</span><span
class="method-args">(accessor, method, ali = method)</span>
<span class="method-click-advice">click to toggle source</span>
</div>
<div class="method-description">
<p>Define <code>method</code> as delegator instance method with an optional alias name <code>ali</code>. <a href="Method.html"><code>Method</code></a> calls to <code>ali</code> will be delegated to <code>accessor.method</code>. <code>accessor</code> should be a method name, instance variable name, or constant name. Use the full path to the constant if providing the constant name. Returns the name of the method defined.</p>
<pre class="ruby"><span class="ruby-keyword">class</span> <span class="ruby-constant">MyQueue</span>
<span class="ruby-constant">CONST</span> = <span class="ruby-value">1</span>
<span class="ruby-identifier">extend</span> <span class="ruby-constant">Forwardable</span>
<span class="ruby-identifier">attr_reader</span> <span class="ruby-value">:queue</span>
<span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">initialize</span>
<span class="ruby-ivar">@queue</span> = []
<span class="ruby-keyword">end</span>
<span class="ruby-identifier">def_delegator</span> <span class="ruby-value">:@queue</span>, <span class="ruby-value">:push</span>, <span class="ruby-value">:mypush</span>
<span class="ruby-identifier">def_delegator</span> <span class="ruby-string">'MyQueue::CONST'</span>, <span class="ruby-value">:to_i</span>
<span class="ruby-keyword">end</span>
<span class="ruby-identifier">q</span> = <span class="ruby-constant">MyQueue</span>.<span class="ruby-identifier">new</span>
<span class="ruby-identifier">q</span>.<span class="ruby-identifier">mypush</span> <span class="ruby-value">42</span>
<span class="ruby-identifier">q</span>.<span class="ruby-identifier">queue</span> <span class="ruby-comment">#=> [42]</span>
<span class="ruby-identifier">q</span>.<span class="ruby-identifier">push</span> <span class="ruby-value">23</span> <span class="ruby-comment">#=> NoMethodError</span>
<span class="ruby-identifier">q</span>.<span class="ruby-identifier">to_i</span> <span class="ruby-comment">#=> 1</span>
</pre>
<div class="method-source-code" id="def_instance_delegator-source">
<pre><span class="ruby-comment"># File lib/forwardable.rb, line 183</span>
<span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">def_instance_delegator</span>(<span class="ruby-identifier">accessor</span>, <span class="ruby-identifier">method</span>, <span class="ruby-identifier">ali</span> = <span class="ruby-identifier">method</span>)
<span class="ruby-identifier">gen</span> = <span class="ruby-constant">Forwardable</span>.<span class="ruby-identifier">_delegator_method</span>(<span class="ruby-keyword">self</span>, <span class="ruby-identifier">accessor</span>, <span class="ruby-identifier">method</span>, <span class="ruby-identifier">ali</span>)
<span class="ruby-comment"># If it's not a class or module, it's an instance</span>
<span class="ruby-identifier">mod</span> = <span class="ruby-constant">Module</span> <span class="ruby-operator">===</span> <span class="ruby-keyword">self</span> <span class="ruby-operator">?</span> <span class="ruby-keyword">self</span> <span class="ruby-operator">:</span> <span class="ruby-identifier">singleton_class</span>
<span class="ruby-identifier">ret</span> = <span class="ruby-identifier">mod</span>.<span class="ruby-identifier">module_eval</span>(<span class="ruby-operator">&</span><span class="ruby-identifier">gen</span>)
<span class="ruby-identifier">mod</span>.<span class="ruby-identifier">send</span>(<span class="ruby-value">:ruby2_keywords</span>, <span class="ruby-identifier">ali</span>) <span class="ruby-keyword">if</span> <span class="ruby-constant">RUBY_VERSION</span> <span class="ruby-operator">>=</span> <span class="ruby-string">'2.7'</span>
<span class="ruby-identifier">ret</span>
<span class="ruby-keyword">end</span></pre>
</div>
</div>
<div class="aliases">
Also aliased as: <a href="Forwardable.html#method-i-def_delegator">def_delegator</a>
</div>
</div>
<div id="method-i-def_instance_delegators" class="method-detail ">
<div class="method-heading">
<span class="method-name">def_instance_delegators</span><span
class="method-args">(accessor, *methods)</span>
<span class="method-click-advice">click to toggle source</span>
</div>
<div class="method-description">
<p>Shortcut for defining multiple delegator methods, but with no provision for using a different name. The following two code samples have the same effect:</p>
<pre class="ruby"><span class="ruby-identifier">def_delegators</span> <span class="ruby-value">:@records</span>, <span class="ruby-value">:size</span>, <span class="ruby-value">:<<</span>, <span class="ruby-value">:map</span>
<span class="ruby-identifier">def_delegator</span> <span class="ruby-value">:@records</span>, <span class="ruby-value">:size</span>
<span class="ruby-identifier">def_delegator</span> <span class="ruby-value">:@records</span>, <span class="ruby-value">:<<</span>
<span class="ruby-identifier">def_delegator</span> <span class="ruby-value">:@records</span>, <span class="ruby-value">:map</span>
</pre>
<div class="method-source-code" id="def_instance_delegators-source">
<pre><span class="ruby-comment"># File lib/forwardable.rb, line 151</span>
<span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">def_instance_delegators</span>(<span class="ruby-identifier">accessor</span>, <span class="ruby-operator">*</span><span class="ruby-identifier">methods</span>)
<span class="ruby-identifier">methods</span>.<span class="ruby-identifier">each</span> <span class="ruby-keyword">do</span> <span class="ruby-operator">|</span><span class="ruby-identifier">method</span><span class="ruby-operator">|</span>
<span class="ruby-keyword">next</span> <span class="ruby-keyword">if</span> <span class="ruby-regexp">/\A__(?:send|id)__\z/</span> <span class="ruby-operator">=~</span> <span class="ruby-identifier">method</span>
<span class="ruby-identifier">def_instance_delegator</span>(<span class="ruby-identifier">accessor</span>, <span class="ruby-identifier">method</span>)
<span class="ruby-keyword">end</span>
<span class="ruby-keyword">end</span></pre>
</div>
</div>
<div class="aliases">
Also aliased as: <a href="Forwardable.html#method-i-def_delegators">def_delegators</a>
</div>
</div>
<div id="method-i-delegate" class="method-detail method-alias">
<div class="method-heading">
<span class="method-name">delegate</span><span
class="method-args">(hash)</span>
</div>
<div class="method-description">
</div>
<div class="aliases">
Alias for: <a href="Forwardable.html#method-i-instance_delegate">instance_delegate</a>
</div>
</div>
<div id="method-i-instance_delegate" class="method-detail ">
<div class="method-heading">
<span class="method-callseq">
delegate method → accessor
</span>
<span class="method-click-advice">click to toggle source</span>
</div>
<div class="method-heading">
<span class="method-callseq">
delegate [method, method, ...] → accessor
</span>
</div>
<div class="method-description">
<p>Takes a hash as its argument. The key is a symbol or an array of symbols. These symbols correspond to method names, instance variable names, or constant names (see <a href="Forwardable.html#method-i-def_delegator"><code>def_delegator</code></a>). The value is the accessor to which the methods will be delegated.</p>
<div class="method-source-code" id="instance_delegate-source">
<pre><span class="ruby-comment"># File lib/forwardable.rb, line 130</span>
<span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">instance_delegate</span>(<span class="ruby-identifier">hash</span>)
<span class="ruby-identifier">hash</span>.<span class="ruby-identifier">each</span> <span class="ruby-keyword">do</span> <span class="ruby-operator">|</span><span class="ruby-identifier">methods</span>, <span class="ruby-identifier">accessor</span><span class="ruby-operator">|</span>
<span class="ruby-keyword">unless</span> <span class="ruby-keyword">defined?</span>(<span class="ruby-identifier">methods</span>.<span class="ruby-identifier">each</span>)
<span class="ruby-identifier">def_instance_delegator</span>(<span class="ruby-identifier">accessor</span>, <span class="ruby-identifier">methods</span>)
<span class="ruby-keyword">else</span>
<span class="ruby-identifier">methods</span>.<span class="ruby-identifier">each</span> {<span class="ruby-operator">|</span><span class="ruby-identifier">method</span><span class="ruby-operator">|</span> <span class="ruby-identifier">def_instance_delegator</span>(<span class="ruby-identifier">accessor</span>, <span class="ruby-identifier">method</span>)}
<span class="ruby-keyword">end</span>
<span class="ruby-keyword">end</span>
<span class="ruby-keyword">end</span></pre>
</div>
</div>
<div class="aliases">
Also aliased as: <a href="Forwardable.html#method-i-delegate">delegate</a>
</div>
</div>
</section>
</section>
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