levovix
/
Nim
镜像来自 https://github.com/nim-lang/Nim


			
				
					
						
						
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270
							<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "https://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!--  This file is generated by Nim. -->
<html xmlns="https://www.w3.org/1999/xhtml" xml:lang="en" lang="en" data-theme="auto">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>std/wrapnils</title>

<!-- Google fonts -->
<link href='https://fonts.googleapis.com/css?family=Lato:400,600,900' rel='stylesheet' type='text/css'/>
<link href='https://fonts.googleapis.com/css?family=Source+Code+Pro:400,500,600' rel='stylesheet' type='text/css'/>

<!-- Favicon -->
<link rel="shortcut icon" href="data:image/x-icon;base64,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"/>
<link rel="icon" type="image/png" sizes="32x32" href="data:image/png;base64,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">

<!-- CSS -->
<link rel="stylesheet" type="text/css" href="nimdoc.out.css?v=2.3.1">

<!-- JS -->
<script type="text/javascript" src="dochack.js?v=2.3.1"></script>
</head>
<body>
  <div class="document" id="documentId">
    <div class="container">
      <h1 class="title">std/wrapnils</h1>
      <div class="row">
  <div class="three columns">
    <div class="theme-select-wrapper">
      <label for="theme-select">Theme:&nbsp;</label>
      <select id="theme-select" onchange="setTheme(this.value)">
        <option value="auto">🌗 Match OS</option>
        <option value="dark">🌑 Dark</option>
        <option value="light">🌕 Light</option>
      </select>
    </div>
    <div id="global-links">
      <ul class="simple-boot">
        <li><a href="manual.html">Manual</a></li>
        <li><a href="lib.html">Standard library</a></li>
        <li> <a id="indexLink" href="theindex.html">Index</a></li>
        <li><a href="compiler/theindex.html">Compiler docs</a></li>
        <li><a href="https://nim-lang.github.io/fusion/theindex.html">Fusion docs</a></li>
        <li><a href="https://nim-lang.github.io/Nim/">devel</a>, <a href="https://nim-lang.org/documentation.html">stable</a></li>
      </ul>
    </div>
    <div id="searchInputDiv">
      Search: <input type="search" id="searchInput"
        oninput="search()" />
    </div>
    
    <ul class="simple simple-toc" id="toc-list">
  <li>
  <a class="reference reference-toplevel" href="#6" id="56">Imports</a>
</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="#%5B%5D%2COption%5BT%5D%2CI" title="`[]`[T, I](a: Option[T]; i: I): auto">`[]`[T, I](a: Option[T]; i: I): auto</a></li>
<li><a class="reference" href="#%5B%5D%2COption%5BU%5D" title="`[]`[U](a: Option[U]): auto">`[]`[U](a: Option[U]): auto</a></li>

</ul>

    </ul>
  </details>
</li>
<li>
  <details open>
    <summary><a class="reference reference-toplevel" href="#17" id="67">Macros</a></summary>
    <ul class="simple simple-toc-section">
      <ul class="simple nested-toc-section">?.
  <li><a class="reference" href="#%3F..m%2Ctyped" title="`?.`(a: typed): auto">`?.`(a: typed): auto</a></li>

</ul>
<ul class="simple nested-toc-section">??.
  <li><a class="reference" href="#%3F%3F..m%2Ctyped" title="`??.`(a: typed): Option">`??.`(a: typed): Option</a></li>

</ul>

    </ul>
  </details>
</li>
<li>
  <details open>
    <summary><a class="reference reference-toplevel" href="#18" id="68">Templates</a></summary>
    <ul class="simple simple-toc-section">
      <ul class="simple nested-toc-section">fakeDot
  <li><a class="reference" href="#fakeDot.t%2COption%2C" title="fakeDot(a: Option; b): untyped">fakeDot(a: Option; b): untyped</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/std/wrapnils.nim#L1" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/std/wrapnils.nim#L1" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

    <div id="tocRoot"></div>
    
    <p class="module-desc">This module allows evaluating expressions safely against the following conditions:<ul class="simple"><li>nil dereferences</li>
<li>field accesses with incorrect discriminant in case objects</li>
</ul>
<p><tt class="docutils literal"><span class="pre"><span class="Identifier">default</span><span class="Punctuation">(</span><span class="Identifier">T</span><span class="Punctuation">)</span></span></tt> is returned in those cases when evaluating an expression of type <tt class="docutils literal"><span class="pre"><span class="Identifier">T</span></span></tt>. This simplifies code by reducing need for if-else branches.</p>
<p>Note: experimental module, unstable API.</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">wrapnils</span>
<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">x1</span><span class="Punctuation">:</span> <span class="Identifier">string</span>
  <span class="Identifier">x2</span><span class="Punctuation">:</span> <span class="Identifier">Foo</span>
  <span class="Identifier">x3</span><span class="Punctuation">:</span> <span class="Keyword">ref</span> <span class="Identifier">int</span>

<span class="Keyword">var</span> <span class="Identifier">f</span><span class="Punctuation">:</span> <span class="Identifier">Foo</span>
<span class="Identifier">assert</span> <span class="Operator">?.</span><span class="Identifier">f</span><span class="Operator">.</span><span class="Identifier">x2</span><span class="Operator">.</span><span class="Identifier">x1</span> <span class="Operator">==</span> <span class="StringLit">&quot;&quot;</span> <span class="Comment"># returns default value since `f` is nil</span>

<span class="Keyword">var</span> <span class="Identifier">f2</span> <span class="Operator">=</span> <span class="Identifier">Foo</span><span class="Punctuation">(</span><span class="Identifier">x1</span><span class="Punctuation">:</span> <span class="StringLit">&quot;a&quot;</span><span class="Punctuation">)</span>
<span class="Identifier">f2</span><span class="Operator">.</span><span class="Identifier">x2</span> <span class="Operator">=</span> <span class="Identifier">f2</span>
<span class="Identifier">assert</span> <span class="Operator">?.</span><span class="Identifier">f2</span><span class="Operator">.</span><span class="Identifier">x1</span> <span class="Operator">==</span> <span class="StringLit">&quot;a&quot;</span> <span class="Comment"># same as f2.x1 (no nil LHS in this chain)</span>
<span class="Identifier">assert</span> <span class="Operator">?.</span><span class="Identifier">Foo</span><span class="Punctuation">(</span><span class="Identifier">x1</span><span class="Punctuation">:</span> <span class="StringLit">&quot;a&quot;</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">x1</span> <span class="Operator">==</span> <span class="StringLit">&quot;a&quot;</span> <span class="Comment"># can use constructor inside</span>

<span class="Comment"># when you know a sub-expression doesn't involve a `nil` (e.g. `f2.x2.x2`),</span>
<span class="Comment"># you can scope it as follows:</span>
<span class="Identifier">assert</span> <span class="Operator">?.</span><span class="Punctuation">(</span><span class="Identifier">f2</span><span class="Operator">.</span><span class="Identifier">x2</span><span class="Operator">.</span><span class="Identifier">x2</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">x3</span><span class="Punctuation">[</span><span class="Punctuation">]</span> <span class="Operator">==</span> <span class="DecNumber">0</span>

<span class="Identifier">assert</span> <span class="Punctuation">(</span><span class="Operator">?.</span><span class="Identifier">f2</span><span class="Operator">.</span><span class="Identifier">x2</span><span class="Operator">.</span><span class="Identifier">x2</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">x3</span> <span class="Operator">==</span> <span class="Keyword">nil</span>  <span class="Comment"># this terminates ?. early</span></pre>
<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">wrapnils</span>
<span class="Comment"># ?. also allows case object</span>
<span class="Keyword">type</span> <span class="Identifier">B</span> <span class="Operator">=</span> <span class="Keyword">object</span>
  <span class="Identifier">b0</span><span class="Punctuation">:</span> <span class="Identifier">int</span>
  <span class="Keyword">case</span> <span class="Identifier">cond</span><span class="Punctuation">:</span> <span class="Identifier">bool</span>
  <span class="Keyword">of</span> <span class="Identifier">false</span><span class="Punctuation">:</span> <span class="Keyword">discard</span>
  <span class="Keyword">of</span> <span class="Identifier">true</span><span class="Punctuation">:</span>
    <span class="Identifier">b1</span><span class="Punctuation">:</span> <span class="Identifier">float</span>

<span class="Keyword">var</span> <span class="Identifier">b</span> <span class="Operator">=</span> <span class="Identifier">B</span><span class="Punctuation">(</span><span class="Identifier">cond</span><span class="Punctuation">:</span> <span class="Identifier">false</span><span class="Punctuation">,</span> <span class="Identifier">b0</span><span class="Punctuation">:</span> <span class="DecNumber">3</span><span class="Punctuation">)</span>
<span class="Identifier">doAssertRaises</span><span class="Punctuation">(</span><span class="Identifier">FieldDefect</span><span class="Punctuation">)</span><span class="Punctuation">:</span> <span class="Keyword">discard</span> <span class="Identifier">b</span><span class="Operator">.</span><span class="Identifier">b1</span> <span class="Comment"># wrong discriminant</span>
<span class="Identifier">doAssert</span> <span class="Operator">?.</span><span class="Identifier">b</span><span class="Operator">.</span><span class="Identifier">b1</span> <span class="Operator">==</span> <span class="FloatNumber">0.0</span> <span class="Comment"># safe</span>
<span class="Identifier">b</span> <span class="Operator">=</span> <span class="Identifier">B</span><span class="Punctuation">(</span><span class="Identifier">cond</span><span class="Punctuation">:</span> <span class="Identifier">true</span><span class="Punctuation">,</span> <span class="Identifier">b1</span><span class="Punctuation">:</span> <span class="FloatNumber">4.5</span><span class="Punctuation">)</span>
<span class="Identifier">doAssert</span> <span class="Operator">?.</span><span class="Identifier">b</span><span class="Operator">.</span><span class="Identifier">b1</span> <span class="Operator">==</span> <span class="FloatNumber">4.5</span>

<span class="Comment"># lvalue semantics are preserved:</span>
<span class="Keyword">if</span> <span class="Punctuation">(</span><span class="Keyword">let</span> <span class="Identifier">p</span> <span class="Operator">=</span> <span class="Operator">?.</span><span class="Identifier">b</span><span class="Operator">.</span><span class="Identifier">b1</span><span class="Operator">.</span><span class="Keyword">addr</span><span class="Punctuation">;</span> <span class="Identifier">p</span> <span class="Operator">!=</span> <span class="Keyword">nil</span><span class="Punctuation">)</span><span class="Punctuation">:</span> <span class="Identifier">p</span><span class="Punctuation">[</span><span class="Punctuation">]</span> <span class="Operator">=</span> <span class="FloatNumber">4.7</span>
<span class="Identifier">doAssert</span> <span class="Identifier">b</span><span class="Operator">.</span><span class="Identifier">b1</span> <span class="Operator">==</span> <span class="FloatNumber">4.7</span></pre></p>
    <div class="section" id="6">
  <h1><a class="toc-backref" href="#6">Imports</a></h1>
  <dl class="item">
    <a class="reference external" href="macros.html">macros</a>, <a class="reference external" href="options.html">options</a>
  </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],I">
  <dt><pre><span class="Keyword">func</span> <a href="#%5B%5D%2COption%5BT%5D%2CI"><span class="Identifier">`[]`</span></a><span class="Other">[</span><span class="Identifier">T</span><span class="Other">,</span> <span class="Identifier">I</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">a</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">i</span><span class="Other">:</span> <span class="Identifier">I</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#auto"><span class="Identifier">auto</span></a> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    See top-level example.
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/std/wrapnils.nim#L178" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/std/wrapnils.nim#L178" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>
<div id="[],Option[U]">
  <dt><pre><span class="Keyword">func</span> <a href="#%5B%5D%2COption%5BU%5D"><span class="Identifier">`[]`</span></a><span class="Other">[</span><span class="Identifier">U</span><span class="Other">]</span><span class="Other">(</span><span class="Identifier">a</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">[</span><span class="Identifier">U</span><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#auto"><span class="Identifier">auto</span></a> {.<span class="Identifier">inline</span>.}</pre></dt>
  <dd>
    
    See top-level example.
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/std/wrapnils.nim#L184" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/std/wrapnils.nim#L184" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>

  </dl>
</div>
<div class="section" id="17">
  <h1><a class="toc-backref" href="#17">Macros</a></h1>
  <dl class="item">
    <div id="?.-macros-all">
  <div id="?..m,typed">
  <dt><pre><span class="Keyword">macro</span> <a href="#%3F..m%2Ctyped"><span class="Identifier">`?.`</span></a><span class="Other">(</span><span class="Identifier">a</span><span class="Other">:</span> <a href="system.html#typed"><span class="Identifier">typed</span></a><span class="Other">)</span><span class="Other">:</span> <a href="system.html#auto"><span class="Identifier">auto</span></a></pre></dt>
  <dd>
    
    Transforms <tt class="docutils literal"><span class="pre"><span class="Identifier">a</span></span></tt> into an expression that can be safely evaluated even in presence of intermediate nil pointers/references, in which case a default value is produced.
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/std/wrapnils.nim#L112" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/std/wrapnils.nim#L112" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>
<div id="??.-macros-all">
  <div id="??..m,typed">
  <dt><pre><span class="Keyword">macro</span> <a href="#%3F%3F..m%2Ctyped"><span class="Identifier">`??.`</span></a><span class="Other">(</span><span class="Identifier">a</span><span class="Other">:</span> <a href="system.html#typed"><span class="Identifier">typed</span></a><span class="Other">)</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a></pre></dt>
  <dd>
    
    Same as <tt class="docutils literal"><span class="pre"><span class="Operator">?.</span></span></tt> but returns an <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="Keyword">import</span> <span class="Identifier">std</span><span class="Operator">/</span><span class="Identifier">options</span>
<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">x1</span><span class="Punctuation">:</span> <span class="Keyword">ref</span> <span class="Identifier">int</span>
  <span class="Identifier">x2</span><span class="Punctuation">:</span> <span class="Identifier">int</span>
<span class="Comment"># `?.` can't distinguish between a valid vs invalid default value, but `??.` can:</span>
<span class="Keyword">var</span> <span class="Identifier">f1</span> <span class="Operator">=</span> <span class="Identifier">Foo</span><span class="Punctuation">(</span><span class="Identifier">x1</span><span class="Punctuation">:</span> <span class="Identifier">int</span><span class="Operator">.</span><span class="Identifier">new</span><span class="Punctuation">,</span> <span class="Identifier">x2</span><span class="Punctuation">:</span> <span class="DecNumber">2</span><span class="Punctuation">)</span>
<span class="Identifier">doAssert</span> <span class="Punctuation">(</span><span class="Operator">??.</span><span class="Identifier">f1</span><span class="Operator">.</span><span class="Identifier">x1</span><span class="Punctuation">[</span><span class="Punctuation">]</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">get</span> <span class="Operator">==</span> <span class="DecNumber">0</span> <span class="Comment"># not enough to tell when the chain was valid.</span>
<span class="Identifier">doAssert</span> <span class="Punctuation">(</span><span class="Operator">??.</span><span class="Identifier">f1</span><span class="Operator">.</span><span class="Identifier">x1</span><span class="Punctuation">[</span><span class="Punctuation">]</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">isSome</span> <span class="Comment"># a nil didn't occur in the chain</span>
<span class="Identifier">doAssert</span> <span class="Punctuation">(</span><span class="Operator">??.</span><span class="Identifier">f1</span><span class="Operator">.</span><span class="Identifier">x2</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">get</span> <span class="Operator">==</span> <span class="DecNumber">2</span>

<span class="Keyword">var</span> <span class="Identifier">f2</span><span class="Punctuation">:</span> <span class="Identifier">Foo</span>
<span class="Identifier">doAssert</span> <span class="Keyword">not</span> <span class="Punctuation">(</span><span class="Operator">??.</span><span class="Identifier">f2</span><span class="Operator">.</span><span class="Identifier">x1</span><span class="Punctuation">[</span><span class="Punctuation">]</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">isSome</span> <span class="Comment"># f2 was nil</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="Keyword">discard</span> <span class="Punctuation">(</span><span class="Operator">??.</span><span class="Identifier">f2</span><span class="Operator">.</span><span class="Identifier">x1</span><span class="Punctuation">[</span><span class="Punctuation">]</span><span class="Punctuation">)</span><span class="Operator">.</span><span class="Identifier">get</span>
<span class="Identifier">doAssert</span> <span class="Operator">?.</span><span class="Identifier">f2</span><span class="Operator">.</span><span class="Identifier">x1</span><span class="Punctuation">[</span><span class="Punctuation">]</span> <span class="Operator">==</span> <span class="DecNumber">0</span> <span class="Comment"># in contrast, this returns default(int)</span></pre>
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/std/wrapnils.nim#L128" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/std/wrapnils.nim#L128" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>

  </dl>
</div>
<div class="section" id="18">
  <h1><a class="toc-backref" href="#18">Templates</a></h1>
  <dl class="item">
    <div id="fakeDot-templates-all">
  <div id="fakeDot.t,Option,">
  <dt><pre><span class="Keyword">template</span> <a href="#fakeDot.t%2COption%2C"><span class="Identifier">fakeDot</span></a><span class="Other">(</span><span class="Identifier">a</span><span class="Other">:</span> <a href="options.html#Option"><span class="Identifier">Option</span></a><span class="Other">;</span> <span class="Identifier">b</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#untyped"><span class="Identifier">untyped</span></a></pre></dt>
  <dd>
    
    See top-level example.
    <a href="https://github.com/nim-lang/Nim/tree/devel/lib/std/wrapnils.nim#L159" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/std/wrapnils.nim#L159" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;

  </dd>
</div>

</div>

  </dl>
</div>

  </div>
</div>

      <div class="twelve-columns footer">
        <span class="nim-sprite"></span>
        <br>
        <small style="color: var(--hint);">Made with Nim. Generated: 2025-02-06 22:28:27 UTC</small>
      </div>
    </div>
  </div>
      <script defer data-domain="nim-lang.org" src="https://plausible.io/js/plausible.js"></script>
    
</body>
</html>