std::bind to a std::function crashes with Clang

Question

I'm having trouble understanding some subtleties when combining std::bind with std::function.

I have minimized my problems to the following code snippet:

#include <functional>
#include <iostream>

void bar(int x) {
    std::cout << "Hello." << std::endl;
}

int main(int argc, char* argv[])
{
    std::function<void(int)> f1 = std::bind(bar, std::placeholders::_1);

    // CRASHES with clang, works fine in VS2010 and VS2012
    std::function<void()> f2 = std::bind(f1, 1);

    f2();

    return 0;
}

Note the explicit conversion to std::function<> (replacing std::function<void()> with auto when constructing f2 works fine).

Creating f2 by copying the f1 object crashes with Clang on OS X (XCode 5.0.1, OS X 10.9 SDK), but works fine with VS2010/VS2012. After a hideously long callstack, the code crashes with a EXC_BAD_ACCESS - note this is when constructing the function object, not when calling it.

Is this a bug in the library implementation or a problem with my code?

A workaround is to explicitly call the operator () member, like this:

std::function<void()> f2 =
    std::bind(&std::function<void(int)>::operator(), f1, 1);

but this comes with a caveat, as it fails to compile on VS2012 (but works in VS2010). This seems to be a bug with VS2012.

Answer 1

Your code works just fine with clang 3.4 (trunk, 194324). It also works with gcc 4.7.2.

I don't get any warnings with -Wall -Wextra -pedantic (except those that complain about the unused x, argc and argv parameters).

It seems as if the clang implementation was buggy in the past but has been fixed.