Question

Can I achieve the same effects without the C++ header <initializer_list>?

Does class initializer_list have to live in namespace std (does the compiler require this)?

I’m fine with a solution that works on the big five (GCC, MSVC, Intel, Clang, Comeau)

Answer 1

It’s tightly coupled as per standard. It’s a wrapper around a compiler-constructed array (though the standard doesn’t say how precisely — GCC uses constructor with pointer and size, MSVC uses constructor with two points). And yes, it’s required to be in namespace std, and in header <initializer_list>.

You’d have to see what constructors they use in each compiler you want to support and replicate that in your version, but TBH, I fail to see the point.

The template std::initializer_list is not predefined; if the header <initializer_list> is not included prior to a use of std::initializer_list — even an implicit use in which the type is not named (7.1.6.4) — the program is ill-formed.

An object of type std::initializer_list<E> is constructed from an initializer list as if the implementation allocated an array of N elements of type E, where N is the number of elements in the initializer list.
Each element of that array is copy-initialized with the corresponding element of the initializer list, and the std::initializer_list<E> object is constructed to refer to that array.