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Module: Concurrent::Concern::Dereferenceable
— Concurrent
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<span class="title">Dereferenceable</span>
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<div id="content"><h1>Module: Concurrent::Concern::Dereferenceable
</h1>
<dl class="box">
<dt class="r1">Included in:</dt>
<dd class="r1"><span class='object_link'><a href="Obligation.html" title="Concurrent::Concern::Obligation (module)">Obligation</a></span>, <span class='object_link'><a href="../MVar.html" title="Concurrent::MVar (class)">MVar</a></span>, <span class='object_link'><a href="../TimerTask.html" title="Concurrent::TimerTask (class)">TimerTask</a></span></dd>
<dt class="r2 last">Defined in:</dt>
<dd class="r2 last">lib/concurrent/concern/dereferenceable.rb</dd>
</dl>
<div class="clear"></div>
<h2>Overview</h2><div class="docstring">
<div class="discussion">
<p>Object references in Ruby are mutable. This can lead to serious problems when
the <code>#value</code> of a concurrent object is a mutable reference. Which is always the
case unless the value is a <code>Fixnum</code>, <code>Symbol</code>, or similar "primitive" data type.
Most classes in this library that expose a <code>#value</code> getter method do so using the
<code>Dereferenceable</code> mixin module.</p>
<h2>Copy Options</h2>
<p>Object references in Ruby are mutable. This can lead to serious
problems when the <span class='object_link'><a href="#value-instance_method" title="Concurrent::Concern::Dereferenceable#value (method)">#value</a></span> of an object is a mutable reference. Which
is always the case unless the value is a <code>Fixnum</code>, <code>Symbol</code>, or similar
"primitive" data type. Each instance can be configured with a few
options that can help protect the program from potentially dangerous
operations. Each of these options can be optionally set when the object
instance is created:</p>
<ul>
<li><code>:dup_on_deref</code> When true the object will call the <code>#dup</code> method on
the <code>value</code> object every time the <code>#value</code> method is called
(default: false)</li>
<li><code>:freeze_on_deref</code> When true the object will call the <code>#freeze</code>
method on the <code>value</code> object every time the <code>#value</code> method is called
(default: false)</li>
<li><code>:copy_on_deref</code> When given a <code>Proc</code> object the <code>Proc</code> will be run
every time the <code>#value</code> method is called. The <code>Proc</code> will be given
the current <code>value</code> as its only argument and the result returned by
the block will be the return value of the <code>#value</code> call. When <code>nil</code>
this option will be ignored (default: nil)</li>
</ul>
<p>When multiple deref options are set the order of operations is strictly defined.
The order of deref operations is:</p>
<ul>
<li><code>:copy_on_deref</code></li>
<li><code>:dup_on_deref</code></li>
<li><code>:freeze_on_deref</code></li>
</ul>
<p>Because of this ordering there is no need to <code>#freeze</code> an object created by a
provided <code>:copy_on_deref</code> block. Simply set <code>:freeze_on_deref</code> to <code>true</code>.
Setting both <code>:dup_on_deref</code> to <code>true</code> and <code>:freeze_on_deref</code> to <code>true</code> is
as close to the behavior of a "pure" functional language (like Erlang, Clojure,
or Haskell) as we are likely to get in Ruby.</p>
</div>
</div>
<div class="tags">
</div>
<h2>
Instance Method Summary
<small>(<a href="#" class="summary_toggle">collapse</a>)</small>
</h2>
<ul class="summary">
<li class="public ">
<span class="summary_signature">
<a href="#value-instance_method" title="#value (instance method)">- (Object) <strong>value</strong> </a>
(also: #deref)
</span>
<span class="summary_desc"><div class='inline'><p>Return the value this object represents after applying the options specified by the <code>#set_deref_options</code> method.</p>
</div></span>
</li>
</ul>
<div id="instance_method_details" class="method_details_list">
<h2>Instance Method Details</h2>
<div class="method_details first">
<h3 class="signature first" id="value-instance_method">
- (<tt>Object</tt>) <strong>value</strong>
<span class="aliases">Also known as:
<span class="names"><span id='deref-instance_method'>deref</span></span>
</span>
</h3><div class="docstring">
<div class="discussion">
<p>Return the value this object represents after applying the options specified
by the <code>#set_deref_options</code> method.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>Object</tt>)</span>
—
<div class='inline'><p>the current value of the object</p>
</div>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
21
22
23</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/concern/dereferenceable.rb', line 21</span>
<span class='kw'>def</span> <span class='id identifier rubyid_value'>value</span>
<span class='id identifier rubyid_synchronize'>synchronize</span> <span class='lbrace'>{</span> <span class='id identifier rubyid_apply_deref_options'>apply_deref_options</span><span class='lparen'>(</span><span class='ivar'>@value</span><span class='rparen'>)</span> <span class='rbrace'>}</span>
<span class='kw'>end</span></pre>
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