http://llvm.org/bugs/show_bug.cgi?id=12153
Bug #: 12153
Summary: Incorrect warning about unused parameter when using
capturing variadic parameter in lambda
Product: clang
Version: trunk
Platform: Macintosh
OS/Version: MacOS X
Status: NEW
Severity: normal
Priority: P
Component: C++0x
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected], [email protected]
Classification: Unclassified
Compiling the following program with clang r151811 results in a warning about
the unused parameter 't':
template <typename... T>
static int count(T... t)
{
auto l = [t...]() { return sizeof...(t); };
return l();
}
$ $ ~/LLVM/build/Release+Asserts/bin/clang++ -std=c++0x -c -Wunused-parameter
-v clang.cpp
clang version 3.1 (trunk 151811)
Target: x86_64-apple-darwin10.8.0
Thread model: posix
[...]
clang.cpp:2:23: warning: unused parameter 't' [-Wunused-parameter]
static int count(T... t)
^
1 warning generated.
The warning does not occur when 't' is not a variadic template parameter (the
two programs are not equivalent, of course):
template <typename T>
static int count(T t)
{
auto l = [&t]() { return sizeof(t); };
return l();
}
Incidentally I was wondering when exactly in this case 't' would count as being
used: When captured by a lambda but not used in the lambda, or when captured
*and* used by a lambda? And should capturing a variable but not using it also
result in a warning? (currently it doesn't)
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