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publishing docs for 0.13.1
2023-12-21 12:54:13 +00:00
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<h1 class="type-name">
<span class="kind">abstract struct</span> Enum
</h1>
<ul class="superclass-hierarchy"><li class="superclass"><a href="Enum.html">Enum</a></li><li class="superclass">Value</li><li class="superclass">Object</li></ul>
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Overview
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<p>Enum is the base type of all enums.</p>
<p>An enum is a set of integer values, where each value has an associated name. For example:</p>
<pre><code class="language-crystal"><span class="k">enum</span> <span class="t">Color</span>
<span class="t">Red</span> <span class="c"># 0</span>
<span class="t">Green</span> <span class="c"># 1</span>
<span class="t">Blue</span> <span class="c"># 2</span>
<span class="k">end</span></code></pre>
<p>Values start with the value <code>0</code> and are incremented by one, but can be overwritten.</p>
<p>To get the underlying value you invoke value on it:</p>
<pre><code class="language-crystal"><span class="t">Color</span><span class="t">::</span><span class="t">Green</span>.value <span class="c"># =&gt; 1</span></code></pre>
<p>Each constant (member) in the enum has the type of the enum:</p>
<pre><code class="language-crystal"><span class="k">typeof</span>(<span class="t">Color</span><span class="t">::</span><span class="t">Red</span>) <span class="c"># =&gt; Color</span></code></pre>
<h3><a id="flags-enum" class="anchor" href="#flags-enum">
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</a>Flags enum</h3>
<p>An enum can be marked with the <code>@[Flags]</code> annotation. This changes the default values:</p>
<pre><code class="language-crystal">@[<span class="t">Flags</span>]
<span class="k">enum</span> <span class="t">IOMode</span>
<span class="t">Read</span> <span class="c"># 1</span>
<span class="t">Write</span> <span class="c"># 2</span>
<span class="t">Async</span> <span class="c"># 4</span>
<span class="k">end</span></code></pre>
<p>Additionally, some methods change their behaviour.</p>
<h3><a id="enums-from-integers" class="anchor" href="#enums-from-integers">
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</a>Enums from integers</h3>
<p>An enum can be created from an integer:</p>
<pre><code class="language-crystal"><span class="t">Color</span>.new(<span class="n">1</span>).to_s <span class="c"># =&gt; &quot;Green&quot;</span></code></pre>
<p>Values that don't correspond to enum's constants are allowed: the value
will still be of type Color, but when printed you will get the underlying value:</p>
<pre><code class="language-crystal"><span class="t">Color</span>.new(<span class="n">10</span>).to_s <span class="c"># =&gt; &quot;10&quot;</span></code></pre>
<p>This method is mainly intended to convert integers from C to enums in Crystal.</p>
<h3><a id="question-methods" class="anchor" href="#question-methods">
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</a>Question methods</h3>
<p>An enum automatically defines question methods for each member, using
<code>String#underscore</code> for the method name.</p>
<ul>
<li>In the case of regular enums, this compares by equality (<code>==</code>).</li>
<li>In the case of flags enums, this invokes <code>includes?</code>.</li>
</ul>
<p>For example:</p>
<pre><code class="language-crystal">color <span class="o">=</span> <span class="t">Color</span><span class="t">::</span><span class="t">Blue</span>
color.red? <span class="c"># =&gt; false</span>
color.blue? <span class="c"># =&gt; true</span>
mode <span class="o">=</span> <span class="t">IOMode</span><span class="t">::</span><span class="t">Read</span> <span class="o">|</span> <span class="t">IOMode</span><span class="t">::</span><span class="t">Async</span>
mode.read? <span class="c"># =&gt; true</span>
mode.write? <span class="c"># =&gt; false</span>
mode.async? <span class="c"># =&gt; true</span></code></pre>
<p>This is very convenient in <code>case</code> expressions:</p>
<pre><code class="language-crystal"><span class="k">case</span> color
<span class="k">when</span> .red?
puts <span class="s">&quot;Got red&quot;</span>
<span class="k">when</span> .blue?
puts <span class="s">&quot;Got blue&quot;</span>
<span class="k">end</span></code></pre>
<h3><a id="changing-the-base-type" class="anchor" href="#changing-the-base-type">
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</a>Changing the Base Type</h3>
<p>The type of the underlying enum value is <code>Int32</code> by default, but it can be changed to any type in <code>Int::Primitive</code>.</p>
<pre><code class="language-crystal"><span class="k">enum</span> <span class="t">Color</span> : <span class="t">UInt8</span>
<span class="t">Red</span>
<span class="t">Green</span>
<span class="t">Blue</span>
<span class="k">end</span>
<span class="t">Color</span><span class="t">::</span><span class="t">Red</span>.value <span class="c"># : UInt8</span></code></pre>
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Included Modules
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Defined in:
</h2>
<a href="https://github.com/crystal-lang/crystal-db/blob/v0.13.1/src/db/result_set.cr#L156" target="_blank">
db/result_set.cr
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<br/>
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Constructors
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<a href="#new%28rs%3ADB%3A%3AResultSet%29%3Aself-class-method" class="signature"><strong>.new</strong>(rs : DB::ResultSet) : <span class="k">self</span></a>
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Constructor Detail
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def self.<strong>new</strong>(rs : <a href="DB/ResultSet.html">DB::ResultSet</a>) : <span class="k">self</span>
<a class="method-permalink" href="#new%28rs%3ADB%3A%3AResultSet%29%3Aself-class-method">#</a>
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[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.13.1/src/db/result_set.cr#L157" target="_blank">View source</a>]
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