Initialising a struct that contains a vector of itself

Question

I have a menu system that I want to initialise from constant data. A MenuItem can contain, as a sub-menu, a vector of MenuItems. But it only works

Answer 1

GMan is correct in his comment: in the declaration of S::v in your code, S is still incomplete. A type must be complete to be usable as the value type in an STL container. For more information see Matt Austern's article "The Standard Librarian: Containers of Incomplete Types."

If you were to switch to a container that is usable with an incomplete type, then your code is fine. For example, given the following:

#include 

template 
struct Container
{
    Container() { }
    Container(std::initializer_list) { }
};

struct S { Container v; };

then your original initialization should work fine:

S s3 = { { { } } } ;

This would work too:

S s4 = { { { { { { { { { { { { { { { { /*zomg*/ } } } } } } } } } } } } } } } };