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<h1 class="title">std/with</h1>
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<a class="reference reference-toplevel" href="#6" id="56">Imports</a>
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<summary><a class="reference reference-toplevel" href="#17" id="67">Macros</a></summary>
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<ul class="simple nested-toc-section">with
<li><a class="reference" href="#with.m%2Ctyped%2Cvarargs%5Buntyped%5D" title="with(arg: typed; calls: varargs[untyped]): untyped">with(arg: typed; calls: varargs[untyped]): untyped</a></li>
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<a href="https://github.com/nim-lang/Nim/tree/devel/lib/std/with.nim#L1" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/std/with.nim#L1" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;
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<p class="module-desc"><p>This module implements the <tt class="docutils literal"><span class="pre"><span class="Identifier">with</span></span></tt> macro for easy function chaining. See <a class="reference external" href="https://github.com/nim-lang/RFCs/issues/193">https://github.com/nim-lang/RFCs/issues/193</a> and <a class="reference external" href="https://github.com/nim-lang/RFCs/issues/192">https://github.com/nim-lang/RFCs/issues/192</a> for details leading to this particular design.</p>
<p><strong>Since:</strong> version 1.2.</p>
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<h1><a class="toc-backref" href="#6">Imports</a></h1>
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<a class="reference external" href="macros.html">macros</a>, <a class="reference external" href="underscored_calls.html">underscored_calls</a>
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<h1><a class="toc-backref" href="#17">Macros</a></h1>
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<div id="with.m,typed,varargs[untyped]">
<dt><pre><span class="Keyword">macro</span> <a href="#with.m%2Ctyped%2Cvarargs%5Buntyped%5D"><span class="Identifier">with</span></a><span class="Other">(</span><span class="Identifier">arg</span><span class="Other">:</span> <a href="system.html#typed"><span class="Identifier">typed</span></a><span class="Other">;</span> <span class="Identifier">calls</span><span class="Other">:</span> <a href="system.html#varargs"><span class="Identifier">varargs</span></a><span class="Other">[</span><a href="system.html#untyped"><span class="Identifier">untyped</span></a><span class="Other">]</span><span class="Other">)</span><span class="Other">:</span> <a href="system.html#untyped"><span class="Identifier">untyped</span></a></pre></dt>
<dd>
This macro provides <span id="chaining_1">chaining</span> of function calls. It does so by patching every call in <tt class="docutils literal"><span class="pre"><span class="Identifier">calls</span></span></tt> to use <tt class="docutils literal"><span class="pre"><span class="Identifier">arg</span></span></tt> as the first argument.<div class="admonition admonition-warning"><span class="admonition-warning-text"><b>Caution:</b></span>
This evaluates <tt class="docutils literal"><span class="pre"><span class="Identifier">arg</span></span></tt> multiple times!</div>
<p><strong class="examples_text">Example:</strong></p>
<pre class="listing"><span class="Keyword">var</span> <span class="Identifier">x</span> <span class="Operator">=</span> <span class="StringLit">&quot;yay&quot;</span>
<span class="Identifier">with</span> <span class="Identifier">x</span><span class="Punctuation">:</span>
<span class="Identifier">add</span> <span class="StringLit">&quot;abc&quot;</span>
<span class="Identifier">add</span> <span class="StringLit">&quot;efg&quot;</span>
<span class="Identifier">doAssert</span> <span class="Identifier">x</span> <span class="Operator">==</span> <span class="StringLit">&quot;yayabcefg&quot;</span>
<span class="Keyword">var</span> <span class="Identifier">a</span> <span class="Operator">=</span> <span class="DecNumber">44</span>
<span class="Identifier">with</span> <span class="Identifier">a</span><span class="Punctuation">:</span>
<span class="Operator">+=</span> <span class="DecNumber">4</span>
<span class="Operator">-=</span> <span class="DecNumber">5</span>
<span class="Identifier">doAssert</span> <span class="Identifier">a</span> <span class="Operator">==</span> <span class="DecNumber">43</span>
<span class="Comment"># Nesting works for object types too!</span>
<span class="Keyword">var</span> <span class="Identifier">foo</span> <span class="Operator">=</span> <span class="Punctuation">(</span><span class="Identifier">bar</span><span class="Punctuation">:</span> <span class="DecNumber">1</span><span class="Punctuation">,</span> <span class="Identifier">qux</span><span class="Punctuation">:</span> <span class="Punctuation">(</span><span class="Identifier">baz</span><span class="Punctuation">:</span> <span class="DecNumber">2</span><span class="Punctuation">)</span><span class="Punctuation">)</span>
<span class="Identifier">with</span> <span class="Identifier">foo</span><span class="Punctuation">:</span>
<span class="Identifier">bar</span> <span class="Operator">=</span> <span class="DecNumber">2</span>
<span class="Identifier">with</span> <span class="Identifier">qux</span><span class="Punctuation">:</span>
<span class="Identifier">baz</span> <span class="Operator">=</span> <span class="DecNumber">3</span>
<span class="Identifier">doAssert</span> <span class="Identifier">foo</span><span class="Operator">.</span><span class="Identifier">bar</span> <span class="Operator">==</span> <span class="DecNumber">2</span>
<span class="Identifier">doAssert</span> <span class="Identifier">foo</span><span class="Operator">.</span><span class="Identifier">qux</span><span class="Operator">.</span><span class="Identifier">baz</span> <span class="Operator">==</span> <span class="DecNumber">3</span></pre>
<a href="https://github.com/nim-lang/Nim/tree/devel/lib/std/with.nim#L19" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/lib/std/with.nim#L19" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;
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