C++11 - Can't define constexpr literal using constexpr function?

Question

I\'ve run into what seems a counterintuitive error, namely, the inability to assign the value of a constexpr function to a constexpr literal (hope

Answer 1

According to the standard, MyClass is considered an incomplete type when you try to invoke FooValue to initialize Foo5. Therefore, you cannot use its members as you did.
The type is considered a completely-defined object type (or complete type) at the closing }.
On the other side, the class is regarded as complete within function bodies. That's why Foo5Alt compiles just fine.
See [class.mem]/6 for further details.