https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64329
Michael Stahl <mstahl at redhat dot com> changed:
What |Removed |Added
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CC| |mstahl at redhat dot com
--- Comment #1 from Michael Stahl <mstahl at redhat dot com> ---
i believe i've hit the same problem, here's the footgun reproducer i came up
with:
#include <functional>
#include <cstdio>
int foo = 42;
int const& bar()
{
return foo;
}
int main()
{
std::function<int const& ()> f{ [] () { return bar(); } };
int const& rfoo = f();
printf("%p %p\n", (void*)&foo, (void*)&rfoo);
return &foo == &rfoo;
}
this is g++ (GCC) 5.3.1 20160406 (Red Hat 5.3.1-6)
> g++ -std=c++11 -Wall -Wextra -pedantic -Weffc++ -W lambdaref.cc && ./a.out
0x60204c (nil)
the problem is that the deduced return type of the lambda is a value
type, never a reference type. this caught me by surprise, but it's
the same rule as for "auto".
if the C++ committee has to make surprising and error-prone type
inference rules, then at least implementations like g++ could
give a warning about returning a reference from a lambda that
is implicitly copied to a value, only to be implicitly converted
again into nothing.
Visual Studio 2013 gives a "warning C4172 returning address of local
variable or temporary" from somewhere inside its std::function code.
