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      <h1 class="title">std/options</h1>
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    <ul class="simple simple-toc" id="toc-list">
  <li><a class="reference" id="basic-usage_toc" href="#basic-usage">Basic usage</a></li>
<li><a class="reference" id="pattern-matching_toc" href="#pattern-matching">Pattern matching</a></li>
<li>
  <a class="reference reference-toplevel" href="#6" id="56">Imports</a>
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  <details open>
    <summary><a class="reference reference-toplevel" href="#7" id="57">Types</a></summary>
    <ul class="simple simple-toc-section">
      <li><a class="reference" href="#Option" title="Option[T] = object
  when T is SomePointer:
  else:">Option</a></li>
<li><a class="reference" href="#UnpackDefect" title="UnpackDefect = object of Defect">UnpackDefect</a></li>
<li><a class="reference" href="#UnpackError" title="UnpackError {.deprecated: &quot;See corresponding Defect&quot;.} = UnpackDefect">UnpackError</a></li>

    </ul>
  </details>
</li>
<li>
  <details open>
    <summary><a class="reference reference-toplevel" href="#12" id="62">Procs</a></summary>
    <ul class="simple simple-toc-section">
      <ul class="simple nested-toc-section">$
  <li><a class="reference" href="#%24%2COption%5BT%5D" title="`$`[T](self: Option[T]): string">`$`[T](self: Option[T]): string</a></li>

</ul>
<ul class="simple nested-toc-section">==
  <li><a class="reference" href="#%3D%3D%2COption%5BT%5D%2COption%5BT%5D" title="`==`[T](a, b: Option[T]): bool">`==`[T](a, b: Option[T]): bool</a></li>

</ul>
<ul class="simple nested-toc-section">filter
  <li><a class="reference" href="#filter%2COption%5BT%5D%2Cproc%28T%29" title="filter[T](self: Option[T]; callback: proc (input: T): bool): Option[T]">filter[T](self: Option[T]; callback: proc (input: T): bool): Option[T]</a></li>

</ul>
<ul class="simple nested-toc-section">flatMap
  <li><a class="reference" href="#flatMap%2COption%5BT%5D%2Cproc%28T%29" title="flatMap[T, R](self: Option[T]; callback: proc (input: T): Option[R]): Option[R]">flatMap[T, R](self: Option[T]; callback: proc (input: T): Option[R]): Option[R]</a></li>

</ul>
<ul class="simple nested-toc-section">flatten
  <li><a class="reference" href="#flatten%2COption%5BOption%5BT%5D%5D" title="flatten[T](self: Option[Option[T]]): Option[T]">flatten[T](self: Option[Option[T]]): Option[T]</a></li>

</ul>
<ul class="simple nested-toc-section">get
  <li><a class="reference" href="#get%2COption%5BT%5D" title="get[T](self: Option[T]): lent T">get[T](self: Option[T]): lent T</a></li>
<li><a class="reference" href="#get%2COption%5BT%5D%2CT" title="get[T](self: Option[T]; otherwise: T): T">get[T](self: Option[T]; otherwise: T): T</a></li>
<li><a class="reference" href="#get%2COption%5BT%5D_2" title="get[T](self: var Option[T]): var T">get[T](self: var Option[T]): var T</a></li>

</ul>
<ul class="simple nested-toc-section">isNone
  <li><a class="reference" href="#isNone%2COption%5BT%5D" title="isNone[T](self: Option[T]): bool">isNone[T](self: Option[T]): bool</a></li>

</ul>
<ul class="simple nested-toc-section">isSome
  <li><a class="reference" href="#isSome%2COption%5BT%5D" title="isSome[T](self: Option[T]): bool">isSome[T](self: Option[T]): bool</a></li>

</ul>
<ul class="simple nested-toc-section">map
  <li><a class="reference" href="#map%2COption%5BT%5D%2Cproc%28T%29_2" title="map[T, R](self: Option[T]; callback: proc (input: T): R): Option[R]">map[T, R](self: Option[T]; callback: proc (input: T): R): Option[R]</a></li>
<li><a class="reference" href="#map%2COption%5BT%5D%2Cproc%28T%29" title="map[T](self: Option[T]; callback: proc (input: T))">map[T](self: Option[T]; callback: proc (input: T))</a></li>

</ul>
<ul class="simple nested-toc-section">none
  <li><a class="reference" href="#none%2Ctypedesc" title="none(T: typedesc): Option[T]">none(T: typedesc): Option[T]</a></li>
<li><a class="reference" href="#none" title="none[T](): Option[T]">none[T](): Option[T]</a></li>

</ul>
<ul class="simple nested-toc-section">option
  <li><a class="reference" href="#option%2CsinkT" title="option[T](val: sink T): Option[T]">option[T](val: sink T): Option[T]</a></li>

</ul>
<ul class="simple nested-toc-section">some
  <li><a class="reference" href="#some%2CsinkT" title="some[T](val: sink T): Option[T]">some[T](val: sink T): Option[T]</a></li>

</ul>
<ul class="simple nested-toc-section">unsafeGet
  <li><a class="reference" href="#unsafeGet%2COption%5BT%5D" title="unsafeGet[T](self: Option[T]): lent T">unsafeGet[T](self: Option[T]): lent T</a></li>

</ul>

    </ul>
  </details>
</li>

</ul>

  </div>
  <div class="nine columns" id="content">
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L1" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L1" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

    <div id="tocRoot"></div>
    
    <p class="module-desc"><p>This module implements types which encapsulate an optional value.</p>
<p>A value of type <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span><span class="Punctuation">[</span><span class="Identifier">T</span><span class="Punctuation">]</span></span></tt> either contains a value <tt class="docutils literal"><span class="pre"><span class="Identifier">x</span></span></tt> (represented as <tt class="docutils literal"><span class="pre"><span class="Identifier">some</span><span class="Punctuation">(</span><span class="Identifier">x</span><span class="Punctuation">)</span></span></tt>) or is empty (<tt class="docutils literal"><span class="pre"><span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">T</span><span class="Punctuation">)</span></span></tt>).</p>
<p>This can be useful when you have a value that can be present or not. The absence of a value is often represented by <tt class="docutils literal"><span class="pre"><span class="Keyword">nil</span></span></tt>, but that is not always available, nor is it always a good solution.</p>

<h1><a class="toc-backref" id="basic-usage" href="#basic-usage">Basic usage</a></h1><p>Let's start with an example: a procedure that finds the index of a character in a string. </p>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">import</span> <span class="Identifier">std</span><span class="Operator">/</span><span class="Identifier">options</span>
<span class="Keyword">proc</span> <span class="Identifier">find</span><span class="Punctuation">(</span><span class="Identifier">haystack</span><span class="Punctuation">:</span> <span class="Identifier">string</span><span class="Punctuation">,</span> <span class="Identifier">needle</span><span class="Punctuation">:</span> <span class="Identifier">char</span><span class="Punctuation">)</span><span class="Punctuation">:</span> <span class="Identifier">Option</span><span class="Punctuation">[</span><span class="Identifier">int</span><span class="Punctuation">]</span> <span class="Operator">=</span>
  <span class="Keyword">for</span> <span class="Identifier">i</span><span class="Punctuation">,</span> <span class="Identifier">c</span> <span class="Keyword">in</span> <span class="Identifier">haystack</span><span class="Punctuation">:</span>
    <span class="Keyword">if</span> <span class="Identifier">c</span> <span class="Operator">==</span> <span class="Identifier">needle</span><span class="Punctuation">:</span>
      <span class="Keyword">return</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="Identifier">i</span><span class="Punctuation">)</span>
  <span class="Keyword">return</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span>  <span class="Comment"># This line is actually optional,</span>
                    <span class="Comment"># because the default is empty</span>

<span class="Keyword">let</span> <span class="Identifier">found</span> <span class="Operator">=</span> <span class="StringLit">&quot;abc&quot;</span><span class="Operator">.</span><span class="Identifier">find</span><span class="Punctuation">(</span><span class="Punctuation">'</span><span class="Identifier">c</span><span class="CharLit">')</span>
<span class="Identifier">assert</span> <span class="Identifier">found</span><span class="Operator">.</span><span class="Identifier">isSome</span> <span class="Keyword">and</span> <span class="Identifier">found</span><span class="Operator">.</span><span class="Identifier">get</span><span class="Punctuation">(</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="DecNumber">2</span></pre>The <tt class="docutils literal"><span class="pre"><span class="Identifier">get</span></span></tt> operation demonstrated above returns the underlying value, or raises <tt class="docutils literal"><span class="pre"><span class="Identifier">UnpackDefect</span></span></tt> if there is no value. Note that <tt class="docutils literal"><span class="pre"><span class="Identifier">UnpackDefect</span></span></tt> inherits from <tt class="docutils literal"><span class="pre"><span class="Identifier">system</span><span class="Operator">.</span><span class="Identifier">Defect</span></span></tt> and should therefore never be caught. Instead, rely on checking if the option contains a value with the <a class="reference external" href="#isSome,Option[T]">isSome</a> and <a class="reference external" href="#isNone,Option[T]">isNone</a> procs.
<h1><a class="toc-backref" id="pattern-matching" href="#pattern-matching">Pattern matching</a></h1><div class="admonition admonition-info"><span class="admonition-info-text"><b>Note:</b></span>
This requires the <a class="reference external" href="https://github.com/nim-lang/fusion">fusion</a> package.</div>
<p><a class="reference external" href="https://nim-lang.github.io/fusion/src/fusion/matching.html">fusion/matching</a> supports pattern matching on <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt>s, with the <tt class="docutils literal"><span class="pre"><span class="Identifier">Some</span><span class="Punctuation">(</span><span class="Operator">&lt;</span><span class="Identifier">pattern</span><span class="Operator">&gt;</span><span class="Punctuation">)</span></span></tt> and <tt class="docutils literal"><span class="pre"><span class="Identifier">None</span><span class="Punctuation">(</span><span class="Punctuation">)</span></span></tt> patterns.</p>
<p><pre class="listing"><span class="Punctuation">{</span><span class="Operator">.</span><span class="Identifier">experimental</span><span class="Punctuation">:</span> <span class="StringLit">&quot;caseStmtMacros&quot;</span><span class="Operator">.</span><span class="Punctuation">}</span>

<span class="Keyword">import</span> <span class="Identifier">fusion</span><span class="Operator">/</span><span class="Identifier">matching</span>

<span class="Keyword">case</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span>
<span class="Keyword">of</span> <span class="Identifier">Some</span><span class="Punctuation">(</span><span class="Operator">@</span><span class="Identifier">a</span><span class="Punctuation">)</span><span class="Punctuation">:</span>
  <span class="Identifier">assert</span> <span class="Identifier">a</span> <span class="Operator">==</span> <span class="DecNumber">42</span>
<span class="Keyword">of</span> <span class="Identifier">None</span><span class="Punctuation">(</span><span class="Punctuation">)</span><span class="Punctuation">:</span>
  <span class="Identifier">assert</span> <span class="Identifier">false</span>

<span class="Identifier">assertMatch</span><span class="Punctuation">(</span><span class="Identifier">some</span><span class="Punctuation">(</span><span class="Identifier">some</span><span class="Punctuation">(</span><span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span><span class="Punctuation">)</span><span class="Punctuation">)</span><span class="Punctuation">,</span> <span class="Identifier">Some</span><span class="Punctuation">(</span><span class="Identifier">Some</span><span class="Punctuation">(</span><span class="Identifier">None</span><span class="Punctuation">(</span><span class="Punctuation">)</span><span class="Punctuation">)</span><span class="Punctuation">)</span><span class="Punctuation">)</span></pre></p>
</p>
    <div class="section" id="6">
  <h1><a class="toc-backref" href="#6">Imports</a></h1>
  <dl class="item">
    <a class="reference external" href="typetraits.html">typetraits</a>, <a class="reference external" href="assertions.html">assertions</a>
  </dl>
</div>
<div class="section" id="7">
  <h1><a class="toc-backref" href="#7">Types</a></h1>
  <dl class="item">
    <div id="Option">
  <dt><pre><a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span> <span class="Other">=</span> <span class="Keyword">object</span>
  <span class="Keyword">when</span> <span class="Identifier">T</span> <span class="Keyword">is</span> <span class="Identifier">SomePointer</span><span class="Other">:</span>
  <span class="Keyword">else</span><span class="Other">:</span></pre></dt>
  <dd>
    
    An optional type that may or may not contain a value of type <tt class="docutils literal"><span class="pre"><span class="Identifier">T</span></span></tt>. When <tt class="docutils literal"><span class="pre"><span class="Identifier">T</span></span></tt> is a a pointer type (<tt class="docutils literal"><span class="pre"><span class="Keyword">ptr</span></span></tt>, <tt class="docutils literal"><span class="pre"><span class="Identifier">pointer</span></span></tt>, <tt class="docutils literal"><span class="pre"><span class="Keyword">ref</span></span></tt>, <tt class="docutils literal"><span class="pre"><span class="Keyword">proc</span></span></tt> or <tt class="docutils literal"><span class="pre"><span class="Keyword">iterator</span> <span class="Punctuation">{</span><span class="Operator">.</span><span class="Identifier">closure</span><span class="Operator">.</span><span class="Punctuation">}</span></span></tt>), <tt class="docutils literal"><span class="pre"><span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">T</span><span class="Punctuation">)</span></span></tt> is represented as <tt class="docutils literal"><span class="pre"><span class="Keyword">nil</span></span></tt>.
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L91" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L91" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>
<div id="UnpackDefect">
  <dt><pre><a href="options.html#UnpackDefect"><span class="Identifier">UnpackDefect</span></a> <span class="Other">=</span> <span class="Keyword">object</span> <span class="Keyword">of</span> <a href="system.html#Defect"><span class="Identifier">Defect</span></a></pre></dt>
  <dd>
    
    
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L101" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L101" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>
<div id="UnpackError">
  <dt><pre><a href="options.html#UnpackError"><span class="Identifier">UnpackError</span></a> {.<span><span class="Other pragmadots">...</span></span><span class="pragmawrap"><span class="Identifier">deprecated</span><span class="Other">:</span> <span class="StringLit">&quot;See corresponding Defect&quot;</span></span>.} <span class="Other">=</span> <a href="options.html#UnpackDefect"><span class="Identifier">UnpackDefect</span></a></pre></dt>
  <dd>
    <div class="deprecation-message">
  <b>Deprecated:</b> See corresponding Defect
</div>

    
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L102" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L102" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

  </dl>
</div>
<div class="section" id="12">
  <h1><a class="toc-backref" href="#12">Procs</a></h1>
  <dl class="item">
    <div id="$-procs-all">
  <div id="$,Option[T]">
  <dt><pre><span class="Keyword">proc</span> <a href="#%24%2COption%5BT%5D"><span class="Identifier">`$`</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#string"><span class="Identifier">string</span></a></pre></dt>
  <dd>
    
    Get the string representation of the <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt>.
<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Identifier">assert</span> <span class="Operator">$</span><span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="StringLit">&quot;some(42)&quot;</span>
<span class="Identifier">assert</span> <span class="Operator">$</span><span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="StringLit">&quot;none(int)&quot;</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L355" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L355" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="==-procs-all">
  <div id="==,Option[T],Option[T]">
  <dt><pre><span class="Keyword">proc</span> <a href="#%3D%3D%2COption%5BT%5D%2COption%5BT%5D"><span class="Identifier">`==`</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">a</span><span class="Other">,</span> <span class="Identifier">b</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#bool"><span class="Identifier">bool</span></a> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    Returns <tt class="docutils literal"><span class="pre"><span class="Identifier">true</span></span></tt> if both <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt>s are <tt class="docutils literal"><span class="pre"><span class="Identifier">none</span></span></tt>, or if they are both <tt class="docutils literal"><span class="pre"><span class="Identifier">some</span></span></tt> and have equal values.
<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">let</span>
  <span class="Identifier">a</span> <span class="Operator">=</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span>
  <span class="Identifier">b</span> <span class="Operator">=</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span>
  <span class="Identifier">c</span> <span class="Operator">=</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span>
  <span class="Identifier">d</span> <span class="Operator">=</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span>

<span class="Identifier">assert</span> <span class="Identifier">a</span> <span class="Operator">==</span> <span class="Identifier">c</span>
<span class="Identifier">assert</span> <span class="Identifier">b</span> <span class="Operator">==</span> <span class="Identifier">d</span>
<span class="Identifier">assert</span> <span class="Keyword">not</span> <span class="Punctuation">(</span><span class="Identifier">a</span> <span class="Operator">==</span> <span class="Identifier">b</span><span class="Punctuation">)</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L336" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L336" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="filter-procs-all">
  <div id="filter,Option[T],proc(T)">
  <dt><pre><span class="Keyword">proc</span> <a href="#filter%2COption%5BT%5D%2Cproc%28T%29"><span class="Identifier">filter</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">;</span> <span class="Identifier">callback</span><span class="Other">:</span> <span class="Keyword">proc</span> <span class="Other">(</span><span class="Identifier">input</span><span class="Other">:</span> <span class="Identifier">T</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#bool"><span class="Identifier">bool</span></a><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span> {.
    <span class="Identifier">inline</span><span class="Other">,</span> <span class="Identifier">effectsOf</span><span class="Other">:</span> <span class="Identifier">callback</span>.}</pre></dt>
  <dd>
    
    <p>Applies a <tt class="docutils literal"><span class="pre"><span class="Identifier">callback</span></span></tt> to the value of the <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt>.</p>
<p>If the <tt class="docutils literal"><span class="pre"><span class="Identifier">callback</span></span></tt> returns <tt class="docutils literal"><span class="pre"><span class="Identifier">true</span></span></tt>, the option is returned as <tt class="docutils literal"><span class="pre"><span class="Identifier">some</span></span></tt>. If it returns <tt class="docutils literal"><span class="pre"><span class="Identifier">false</span></span></tt>, it is returned as <tt class="docutils literal"><span class="pre"><span class="Identifier">none</span></span></tt>.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#flatMap,Option[A],proc(A)">flatMap proc</a></li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">proc</span> <span class="Identifier">isEven</span><span class="Punctuation">(</span><span class="Identifier">x</span><span class="Punctuation">:</span> <span class="Identifier">int</span><span class="Punctuation">)</span><span class="Punctuation">:</span> <span class="Identifier">bool</span> <span class="Operator">=</span>
  <span class="Identifier">x</span> <span class="Keyword">mod</span> <span class="DecNumber">2</span> <span class="Operator">==</span> <span class="DecNumber">0</span>

<span class="Identifier">assert</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">filter</span><span class="Punctuation">(</span><span class="Identifier">isEven</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span>
<span class="Identifier">assert</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">filter</span><span class="Punctuation">(</span><span class="Identifier">isEven</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span>
<span class="Identifier">assert</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="Operator">-</span><span class="DecNumber">11</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">filter</span><span class="Punctuation">(</span><span class="Identifier">isEven</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L315" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L315" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="flatMap-procs-all">
  <div id="flatMap,Option[T],proc(T)">
  <dt><pre><span class="Keyword">proc</span> <a href="#flatMap%2COption%5BT%5D%2Cproc%28T%29"><span class="Identifier">flatMap</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">,</span> <span class="Identifier">R</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">;</span> <span class="Identifier">callback</span><span class="Other">:</span> <span class="Keyword">proc</span> <span class="Other">(</span><span class="Identifier">input</span><span class="Other">:</span> <span class="Identifier">T</span><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">R</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span>
    <span class="Identifier">R</span><span class="Other">]</span> {.<span class="Identifier">inline</span><span class="Other">,</span> <span class="Identifier">effectsOf</span><span class="Other">:</span> <span class="Identifier">callback</span>.}</pre></dt>
  <dd>
    
    <p>Applies a <tt class="docutils literal"><span class="pre"><span class="Identifier">callback</span></span></tt> function to the value of the <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> and returns the new value.</p>
<p>If the <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> has no value, <tt class="docutils literal"><span class="pre"><span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">R</span><span class="Punctuation">)</span></span></tt> will be returned.</p>
<p>This is similar to <tt class="docutils literal"><span class="pre"><span class="Identifier">map</span></span></tt>, with the difference that the <tt class="docutils literal"><span class="pre"><span class="Identifier">callback</span></span></tt> returns an <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt>, not a raw value. This allows multiple procs with a signature of <tt class="docutils literal"><span class="pre"><span class="Identifier">A</span> <span class="Operator">-&gt;</span> <span class="Identifier">Option</span><span class="Punctuation">[</span><span class="Identifier">B</span><span class="Punctuation">]</span></span></tt> to be chained together.</p>
<p>See also:</p>
<ul class="simple"><li><a class="reference external" href="#flatten,Option[Option[A]]">flatten proc</a></li>
<li><a class="reference external" href="#filter,Option[T],proc(T)">filter proc</a></li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">proc</span> <span class="Identifier">doublePositives</span><span class="Punctuation">(</span><span class="Identifier">x</span><span class="Punctuation">:</span> <span class="Identifier">int</span><span class="Punctuation">)</span><span class="Punctuation">:</span> <span class="Identifier">Option</span><span class="Punctuation">[</span><span class="Identifier">int</span><span class="Punctuation">]</span> <span class="Operator">=</span>
  <span class="Keyword">if</span> <span class="Identifier">x</span> <span class="Operator">&gt;</span> <span class="DecNumber">0</span><span class="Punctuation">:</span>
    <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">2</span> <span class="Operator">*</span> <span class="Identifier">x</span><span class="Punctuation">)</span>
  <span class="Keyword">else</span><span class="Punctuation">:</span>
    <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span>

<span class="Identifier">assert</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">flatMap</span><span class="Punctuation">(</span><span class="Identifier">doublePositives</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">84</span><span class="Punctuation">)</span>
<span class="Identifier">assert</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">flatMap</span><span class="Punctuation">(</span><span class="Identifier">doublePositives</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span>
<span class="Identifier">assert</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="Operator">-</span><span class="DecNumber">11</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">flatMap</span><span class="Punctuation">(</span><span class="Identifier">doublePositives</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L289" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L289" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="flatten-procs-all">
  <div id="flatten,Option[Option[T]]">
  <dt><pre><span class="Keyword">proc</span> <a href="#flatten%2COption%5BOption%5BT%5D%5D"><span class="Identifier">flatten</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    <p>Remove one level of structure in a nested <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt>.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#flatMap,Option[T],proc(T)">flatMap proc</a></li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Identifier">assert</span> <span class="Identifier">flatten</span><span class="Punctuation">(</span><span class="Identifier">some</span><span class="Punctuation">(</span><span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Punctuation">)</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span>
<span class="Identifier">assert</span> <span class="Identifier">flatten</span><span class="Punctuation">(</span><span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">Option</span><span class="Punctuation">[</span><span class="Identifier">int</span><span class="Punctuation">]</span><span class="Punctuation">)</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L275" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L275" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="get-procs-all">
  <div id="get,Option[T]">
  <dt><pre><span class="Keyword">proc</span> <a href="#get%2COption%5BT%5D"><span class="Identifier">get</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#lent"><span class="Identifier">lent</span></a> <span class="Identifier">T</span> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    <p>Returns the content of an <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt>. If it has no value, an <tt class="docutils literal"><span class="pre"><span class="Identifier">UnpackDefect</span></span></tt> exception is raised.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#get,Option[T],T">get proc</a> with a default return value</li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Identifier">assert</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">get</span> <span class="Operator">==</span> <span class="DecNumber">42</span>
<span class="Identifier">doAssertRaises</span><span class="Punctuation">(</span><span class="Identifier">UnpackDefect</span><span class="Punctuation">)</span><span class="Punctuation">:</span>
  <span class="Identifier">echo</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">string</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">get</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L191" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L191" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>
<div id="get,Option[T],T">
  <dt><pre><span class="Keyword">proc</span> <a href="#get%2COption%5BT%5D%2CT"><span class="Identifier">get</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">;</span> <span class="Identifier">otherwise</span><span class="Other">:</span> <span class="Identifier">T</span><span class="Other">)</span><span class="Other">:</span> <span class="Identifier">T</span> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    Returns the content of the <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> or <tt class="docutils literal"><span class="pre"><span class="Identifier">otherwise</span></span></tt> if the <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> has no value.
<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Identifier">assert</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">get</span><span class="Punctuation">(</span><span class="DecNumber">9999</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="DecNumber">42</span>
<span class="Identifier">assert</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">get</span><span class="Punctuation">(</span><span class="DecNumber">9999</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="DecNumber">9999</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L206" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L206" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>
<div id="get,Option[T]_2">
  <dt><pre><span class="Keyword">proc</span> <a href="#get%2COption%5BT%5D_2"><span class="Identifier">get</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <span class="Keyword">var</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <span class="Keyword">var</span> <span class="Identifier">T</span> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    Returns the content of the <tt class="docutils literal"><span class="pre"><span class="Keyword">var</span> <span class="Identifier">Option</span></span></tt> mutably. If it has no value, an <tt class="docutils literal"><span class="pre"><span class="Identifier">UnpackDefect</span></span></tt> exception is raised.
<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">var</span>
  <span class="Identifier">a</span> <span class="Operator">=</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span>
  <span class="Identifier">b</span> <span class="Operator">=</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">string</span><span class="Punctuation">)</span>
<span class="Identifier">inc</span><span class="Punctuation">(</span><span class="Identifier">a</span><span class="Operator">.</span><span class="Identifier">get</span><span class="Punctuation">)</span>
<span class="Identifier">assert</span> <span class="Identifier">a</span><span class="Operator">.</span><span class="Identifier">get</span> <span class="Operator">==</span> <span class="DecNumber">43</span>
<span class="Identifier">doAssertRaises</span><span class="Punctuation">(</span><span class="Identifier">UnpackDefect</span><span class="Punctuation">)</span><span class="Punctuation">:</span>
  <span class="Identifier">echo</span> <span class="Identifier">b</span><span class="Operator">.</span><span class="Identifier">get</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L218" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L218" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="isNone-procs-all">
  <div id="isNone,Option[T]">
  <dt><pre><span class="Keyword">proc</span> <a href="#isNone%2COption%5BT%5D"><span class="Identifier">isNone</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#bool"><span class="Identifier">bool</span></a> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    <p>Checks if an <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> is empty.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#isSome,Option[T]">isSome proc</a></li>
<li><a class="reference external" href="#none,typedesc">none proc</a></li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Identifier">assert</span> <span class="Keyword">not</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">isNone</span>
<span class="Identifier">assert</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">string</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">isNone</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L176" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L176" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="isSome-procs-all">
  <div id="isSome,Option[T]">
  <dt><pre><span class="Keyword">proc</span> <a href="#isSome%2COption%5BT%5D"><span class="Identifier">isSome</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#bool"><span class="Identifier">bool</span></a> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    <p>Checks if an <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> contains a value.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#isNone,Option[T]">isNone proc</a></li>
<li><a class="reference external" href="#some,T">some proc</a></li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Identifier">assert</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">isSome</span>
<span class="Identifier">assert</span> <span class="Keyword">not</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">string</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">isSome</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L161" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L161" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="map-procs-all">
  <div id="map,Option[T],proc(T)_2">
  <dt><pre><span class="Keyword">proc</span> <a href="#map%2COption%5BT%5D%2Cproc%28T%29_2"><span class="Identifier">map</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">,</span> <span class="Identifier">R</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">;</span> <span class="Identifier">callback</span><span class="Other">:</span> <span class="Keyword">proc</span> <span class="Other">(</span><span class="Identifier">input</span><span class="Other">:</span> <span class="Identifier">T</span><span class="Other">)</span><span class="Other">:</span> <span class="Identifier">R</span><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">R</span><span class="Other">]</span> {.
    <span class="Identifier">inline</span><span class="Other">,</span> <span class="Identifier">effectsOf</span><span class="Other">:</span> <span class="Identifier">callback</span>.}</pre></dt>
  <dd>
    
    <p>Applies a <tt class="docutils literal"><span class="pre"><span class="Identifier">callback</span></span></tt> function to the value of the <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> and returns an <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> containing the new value.</p>
<p>If the <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> has no value, <tt class="docutils literal"><span class="pre"><span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">R</span><span class="Punctuation">)</span></span></tt> will be returned.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#map,Option[T],proc(T)">map proc</a></li>
<li><a class="reference external" href="#flatMap,Option[T],proc(T)">flatMap proc</a> for a version with a callback that returns an <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt></li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">proc</span> <span class="Identifier">isEven</span><span class="Punctuation">(</span><span class="Identifier">x</span><span class="Punctuation">:</span> <span class="Identifier">int</span><span class="Punctuation">)</span><span class="Punctuation">:</span> <span class="Identifier">bool</span> <span class="Operator">=</span>
  <span class="Identifier">x</span> <span class="Keyword">mod</span> <span class="DecNumber">2</span> <span class="Operator">==</span> <span class="DecNumber">0</span>

<span class="Identifier">assert</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">map</span><span class="Punctuation">(</span><span class="Identifier">isEven</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="Identifier">true</span><span class="Punctuation">)</span>
<span class="Identifier">assert</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">map</span><span class="Punctuation">(</span><span class="Identifier">isEven</span><span class="Punctuation">)</span> <span class="Operator">==</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">bool</span><span class="Punctuation">)</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L253" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L253" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>
<div id="map,Option[T],proc(T)">
  <dt><pre><span class="Keyword">proc</span> <a href="#map%2COption%5BT%5D%2Cproc%28T%29"><span class="Identifier">map</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">;</span> <span class="Identifier">callback</span><span class="Other">:</span> <span class="Keyword">proc</span> <span class="Other">(</span><span class="Identifier">input</span><span class="Other">:</span> <span class="Identifier">T</span><span class="Other">)</span><span class="Other">)</span> {.<span class="Identifier">inline</span><span class="Other">,</span>
    <span class="Identifier">effectsOf</span><span class="Other">:</span> <span class="Identifier">callback</span>.}</pre></dt>
  <dd>
    
    <p>Applies a <tt class="docutils literal"><span class="pre"><span class="Identifier">callback</span></span></tt> function to the value of the <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt>, if it has one.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#map,Option[T],proc(T)_2">map proc</a> for a version with a callback which returns a value</li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">var</span> <span class="Identifier">d</span> <span class="Operator">=</span> <span class="DecNumber">0</span>
<span class="Keyword">proc</span> <span class="Identifier">saveDouble</span><span class="Punctuation">(</span><span class="Identifier">x</span><span class="Punctuation">:</span> <span class="Identifier">int</span><span class="Punctuation">)</span> <span class="Operator">=</span>
  <span class="Identifier">d</span> <span class="Operator">=</span> <span class="DecNumber">2</span> <span class="Operator">*</span> <span class="Identifier">x</span>

<span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">map</span><span class="Punctuation">(</span><span class="Identifier">saveDouble</span><span class="Punctuation">)</span>
<span class="Identifier">assert</span> <span class="Identifier">d</span> <span class="Operator">==</span> <span class="DecNumber">0</span>
<span class="Identifier">some</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">map</span><span class="Punctuation">(</span><span class="Identifier">saveDouble</span><span class="Punctuation">)</span>
<span class="Identifier">assert</span> <span class="Identifier">d</span> <span class="Operator">==</span> <span class="DecNumber">84</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L234" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L234" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="none-procs-all">
  <div id="none,typedesc">
  <dt><pre><span class="Keyword">proc</span> <a href="#none%2Ctypedesc"><span class="Identifier">none</span></a><span class="Other">(</span><span class="Identifier">T</span><span class="Other">:</span> <a href="system.html#typedesc"><span class="Identifier">typedesc</span></a><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    <p>Returns an <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> for this type that has no value.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#option,T">option proc</a></li>
<li><a class="reference external" href="#some,T">some proc</a></li>
<li><a class="reference external" href="#isNone,Option[T]">isNone proc</a></li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Identifier">assert</span> <span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">int</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">isNone</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L144" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L144" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>
<div id="none">
  <dt><pre><span class="Keyword">proc</span> <a href="#none"><span class="Identifier">none</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    Alias for <a class="reference external" href="#none,typedesc">none(T)</a>.
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L157" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L157" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="option-procs-all">
  <div id="option,sinkT">
  <dt><pre><span class="Keyword">proc</span> <a href="#option%2CsinkT"><span class="Identifier">option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">val</span><span class="Other">:</span> <a href="system.html#sink"><span class="Identifier">sink</span></a> <span class="Identifier">T</span><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    <p>Can be used to convert a pointer type (<tt class="docutils literal"><span class="pre"><span class="Keyword">ptr</span></span></tt>, <tt class="docutils literal"><span class="pre"><span class="Identifier">pointer</span></span></tt>, <tt class="docutils literal"><span class="pre"><span class="Keyword">ref</span></span></tt> or <tt class="docutils literal"><span class="pre"><span class="Keyword">proc</span></span></tt>) to an option type. It converts <tt class="docutils literal"><span class="pre"><span class="Keyword">nil</span></span></tt> to <tt class="docutils literal"><span class="pre"><span class="Identifier">none</span><span class="Punctuation">(</span><span class="Identifier">T</span><span class="Punctuation">)</span></span></tt>. When <tt class="docutils literal"><span class="pre"><span class="Identifier">T</span></span></tt> is no pointer type, this is equivalent to <tt class="docutils literal"><span class="pre"><span class="Identifier">some</span><span class="Punctuation">(</span><span class="Identifier">val</span><span class="Punctuation">)</span></span></tt>.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#some,T">some proc</a></li>
<li><a class="reference external" href="#none,typedesc">none proc</a></li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">type</span>
  <span class="Identifier">Foo</span> <span class="Operator">=</span> <span class="Keyword">ref</span> <span class="Keyword">object</span>
    <span class="Identifier">a</span><span class="Punctuation">:</span> <span class="Identifier">int</span>
    <span class="Identifier">b</span><span class="Punctuation">:</span> <span class="Identifier">string</span>

<span class="Identifier">assert</span> <span class="Identifier">option</span><span class="Punctuation">[</span><span class="Identifier">Foo</span><span class="Punctuation">]</span><span class="Punctuation">(</span><span class="Keyword">nil</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">isNone</span>
<span class="Identifier">assert</span> <span class="Identifier">option</span><span class="Punctuation">(</span><span class="DecNumber">42</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">isSome</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L104" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L104" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="some-procs-all">
  <div id="some,sinkT">
  <dt><pre><span class="Keyword">proc</span> <a href="#some%2CsinkT"><span class="Identifier">some</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">val</span><span class="Other">:</span> <a href="system.html#sink"><span class="Identifier">sink</span></a> <span class="Identifier">T</span><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    <p>Returns an <tt class="docutils literal"><span class="pre"><span class="Identifier">Option</span></span></tt> that has the value <tt class="docutils literal"><span class="pre"><span class="Identifier">val</span></span></tt>.</p>
<p><strong>See also:</strong></p>
<ul class="simple"><li><a class="reference external" href="#option,T">option proc</a></li>
<li><a class="reference external" href="#none,typedesc">none proc</a></li>
<li><a class="reference external" href="#isSome,Option[T]">isSome proc</a></li>
</ul>

<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">let</span> <span class="Identifier">a</span> <span class="Operator">=</span> <span class="Identifier">some</span><span class="Punctuation">(</span><span class="StringLit">&quot;abc&quot;</span><span class="Punctuation">)</span>

<span class="Identifier">assert</span> <span class="Identifier">a</span><span class="Operator">.</span><span class="Identifier">isSome</span>
<span class="Identifier">assert</span> <span class="Identifier">a</span><span class="Operator">.</span><span class="Identifier">get</span> <span class="Operator">==</span> <span class="StringLit">&quot;abc&quot;</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L125" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L125" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="unsafeGet-procs-all">
  <div id="unsafeGet,Option[T]">
  <dt><pre><span class="Keyword">proc</span> <a href="#unsafeGet%2COption%5BT%5D"><span class="Identifier">unsafeGet</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">self</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#lent"><span class="Identifier">lent</span></a> <span class="Identifier">T</span> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    <p>Returns the value of a <tt class="docutils literal"><span class="pre"><span class="Identifier">some</span></span></tt>. The behavior is undefined for <tt class="docutils literal"><span class="pre"><span class="Identifier">none</span></span></tt>.</p>
<p><strong>Note:</strong> Use this only when you are <strong>absolutely sure</strong> the value is present (e.g. after checking with <a class="reference external" href="#isSome,Option[T]">isSome</a>). Generally, using the <a class="reference external" href="#get,Option[T]">get proc</a> is preferred.</p>

    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/pure/options.nim#L374" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/pure/options.nim#L374" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>

  </dl>
</div>

  </div>
</div>

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