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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Regression: Lambda with no return behaves differently from lambda with empty return"
href="https://llvm.org/bugs/show_bug.cgi?id=24989">24989</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Regression: Lambda with no return behaves differently from lambda with empty return
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.7
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C++14
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>kenton@sandstorm.io
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The code below worked in Clang 3.6 but fails to compile in 3.7. This in
particular is breaking some code that uses Cap'n Proto.
It appears Clang 3.7 treats "[]()(auto) {}" differently from "[]()(auto)
{return;}", even though they are clearly equivalent. In the former case, in
some scenarios (but not all), it fails to recognize that the return type is
"void".
==== TEST CASE ====
// compile with:
// clang --std=c++14 -c test.cc
template <typename R, typename C, typename P>
void match(R (C::*p)(P) const) {}
template <typename Func>
void matchFunctor(Func&& func) {
typedef decltype(func(1)) ReturnType;
match<ReturnType, Func, int&&>(&Func::operator());
}
void f() {
matchFunctor([](auto) {}); // ERROR in clang 3.7, works in 3.6-
matchFunctor([](auto) {return;}); // works in all versions
}
=== OUTPUT ===
test.cc:10:3: error: no matching function for call to 'match'
match<ReturnType, Func, int&&>(&Func::operator());
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cc:14:3: note: in instantiation of function template specialization
'matchFunctor<(lambda at test.cc:14:16)>' requested here
matchFunctor([](auto) {}); // ERROR in clang 3.7, works in 3.6-
^
test.cc:5:6: note: candidate function [with R = void, C = (lambda at
test.cc:14:16), P = int &&] not viable: no overload of 'operator()' matching
'void ((lambda at test.cc:14:16)::*)(int &&) const' for 1st argument
void match(R (C::*p)(P) const) {}
^
1 error generated.</pre>
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