lambda as a static member

Question

I'm trying to use a lambda as a static member, like this:

struct A
{
    static constexpr auto F = [](){};
};


int main()
{
    A::F();
    return 0;
}

Is this even correct C++11 code? On clang, I get this error:

error: constexpr variable 'F' must be initialized by a constant
      expression
    static constexpr auto F = [](){};
                              ^~~~~~

It seems in clang, lambdas aren't considered a constant expression. Is this correct? Perhaps they haven't fully implemented lambdas yet in clang because gcc 4.7 seems to allow it as a constexpr, but it give another error:

error: ‘constexpr const A::F’, declared using local type ‘const’, is used but never defined

I'm not sure, I understand what that means. It seems to correctly deduce the type of the lambda, but it only declares it and not define it. How would I go about defining it?

lambda as a static member

2 Answers