Default-initable Protocol

[xwu (Xiaodi Wu)]

[Pitch] Add the DefaultConstructible protocol to the standard library

This protocol is present in C++ http://en.cppreference.com/w/cpp/concept/DefaultConstructible as well as in Rust std::default - Rust It's the identity element/unit of a monoid or a zero. The Swift implementation is very simple (I'm open to different names) protocol DefaultConstructible {     init() } A lot of the standard types could then be made to conform to this protocol. These include all the numeric types, collection types (array, set, dict), string, basically at least every type …