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describe the preferred approach to silencing 'unused variable warnings' due to asserts.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118863 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2010-11-12 00:19:41 +00:00
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docs/CodingStandards.html
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@ -851,6 +851,38 @@ return 0;
</pre>
</div>
<p>Another issue is that values used only by assertions will produce an "unused
value" warning when assertions are disabled. For example, this code will warn:
</p>
<div class="doc_code">
<pre>
unsigned Size = V.size();
assert(Size &gt; 42 &amp;&amp; "Vector smaller than it should be");
bool NewToSet = Myset.insert(Value);
assert(NewToSet &amp;&amp; "The value shouldn't be in the set yet");
</pre>
</div>
<p>These are two interesting different cases: in the first case, the call to
V.size() is only useful for the assert, and we don't want it executed when
assertions are disabled. Code like this should move the call into the assert
itself. In the second case, the side effects of the call must happen whether
the assert is enabled or not. In this case, the value should be cast to void
to disable the warning. To be specific, it is preferred to write the code
like this:</p>
<div class="doc_code">
<pre>
assert(V.size() &gt; 42 &amp;&amp; "Vector smaller than it should be");
bool NewToSet = Myset.insert(Value); (void)NewToSet;
assert(NewToSet &amp;&amp; "The value shouldn't be in the set yet");
</pre>
</div>
</div>
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