http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56537
Bug #: 56537
Summary: [C++11] lambda expression treats members as const
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: martin.vgag...@gmx.net
The following code won't compile on GCC 4.7.2:
#include <vector>
template<typename T> struct Foo {
std::vector<int> member;
Foo() {
auto f = [this]() {
#if 0
this->
#endif
member.push_back(42);
};
};
};
void bar() { Foo<int> foo; }
The compiler reports:
foo.cc: In lambda function:
foo.cc:9:26: error: no matching function for call to
‘std::vector<int>::push_back(int) const’
foo.cc:9:26: note: candidates are:
In file included from …/4.7.2/include/g++-v4/vector:65:0,
from foo.cc:1:
…/4.7.2/include/g++-v4/bits/stl_vector.h:881:7: note: void std::vector<_Tp,
_Alloc>::push_back(const value_type&) [with _Tp = int; _Alloc =
std::allocator<int>; std::vector<_Tp, _Alloc>::value_type = int] <near match>
…/4.7.2/include/g++-v4/bits/stl_vector.h:881:7: note: no known conversion for
implicit ‘this’ parameter from ‘const std::vector<int>*’ to ‘std::vector<int>*’
…/4.7.2/include/g++-v4/bits/stl_vector.h:899:7: note: void std::vector<_Tp,
_Alloc>::push_back(std::vector<_Tp, _Alloc>::value_type&&) [with _Tp = int;
_Alloc = std::allocator<int>; std::vector<_Tp, _Alloc>::value_type = int] <near
match>
…/4.7.2/include/g++-v4/bits/stl_vector.h:899:7: note: no known conversion for
implicit ‘this’ parameter from ‘const std::vector<int>*’ to ‘std::vector<int>*’
But the "this" parameter in this case is a "Foo* const", not a "const
std::vector<int>*". There are several ways to avoid this problem: one can
enable the "this->" prefix currently disabled using the preprocessor. Or one
can make the whole lambda mutable. But as this appears to be a strange corner
case only encountered in the interplay of several templates, I doubt that this
is intended behaviour.
