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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang should warn for not initializing field in a move constructor"
href="http://bugs.llvm.org/show_bug.cgi?id=32427">32427</a>
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<th>Summary</th>
<td>Clang should warn for not initializing field in a move constructor
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>hughbellars@gmail.com
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<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>The C++ standard states that a move constructor is called when returning a
value from a method unless the compiler is able to elide the move,
For example, the following code invokes undefined behaviour:
#include <iostream>
class CallEmission {
public:
bool assumedPlusZeroSelf;
CallEmission(bool assumedPlusZeroSelf) :
assumedPlusZeroSelf(assumedPlusZeroSelf) {}
CallEmission(CallEmission &&e) {
std::cout << "Called move constructor" << "\n";
}
};
CallEmission method() {
CallEmission x(false);
return x;
}
int main() {
CallEmission x = method();
std::cout << x.assumedPlusZeroSelf;
}
MSVC:
<span class="quote">> Called move constructor
> 140</span >
Clang:
<span class="quote">> 0</span >
This is because with MSVC the move constructor is called, which fails to
initialize the memory of `assumedPlusZeroSelf`.
This caused a crash in Swift on Windows with MSVC
(<a href="https://github.com/apple/swift/pull/8337">https://github.com/apple/swift/pull/8337</a>)
Michael Gottesman, an engineer on the Swift team said "@hughbe Nice find! I
wonder if there is a warning for this.". Seemingly there is not, so it would be
nice to issue a warning here to prevent different behaviour on different
compilers.
Maybe something like "field assumedPlusZeroSelf is not initialized in
constructor CallEmission(CallEmission&&)"</pre>
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