Will C++0x support __stdcall or extern “C” capture-nothing lambdas?

Question

Yesterday I was thinking about whether it would be possible to use the convenience of C++0x lambda functions to write callbacks for Windows API functions.

For exampl

Answer 1

Lambdas without a capture are implicitly convertible to a pointer to function (by a non-explicit conversion function defined by the closure type).

The FCD does not seem to specify what language linkage the function type of that function pointer type has, so if you need to pass this function pointer to C functions, the calling convention of C++ functions and C functions need to be the same. I believe that on Windows, that is the case though. So you should be able to pass the lambda to Windows API functions

typedef void(*callbackType)(void *userData);
extern "C" void someCFunction(callbackType callback);

int main() {
  someCFunction([](void *userData) { /* ... */ });
}

FCD wording at 5.1.2/6:

The closure type for a lambda-expression with no lambda-capture has a public non-virtual non-explicit const conversion function to pointer to function having the same parameter and return types as the closure type’s function call operator. The value returned by this conversion function shall be the address of a function that, when invoked, has the same effect as invoking the closure type’s function call operator.

I think the final Standard should have a note that says that there is a conversion function to both C linkage function pointers and C++ linkage function pointers, as convertibility to C function pointers is one of the goal of this functionality.