> a similar type, but whose size and capacity are fixed on construction and never change.
replyThere is std::array for that. Also, for a type with fixed capacity but variable (up to that capacity) size, we're getting std::inplace_vector soon™.
std::array requires the size to be set at compile-time, while I was talking about arrays whose size is determined at construction-time. Of course std::array is also quite the useful class :-)
replyWhat operations could such frozen vector offer that std::vector does not? If there are none, it doesn't need a separate data structure.
replyOh, on the contrary, the separate structure is needed and useful because it offers _less_, not more:
reply* APIs/function signatures explain more clearly what are the intended uses of the structure that's passed.
* More potential for compiler optimization
* Some potential for having these on the stack (if the compiler deduces the size already at compile-time)
* More convenient for static analysis
* No plethora of confusing constructors (including the infernal two-element ctors which can be misinterpreted super-easily)
etc.