Is there a way to enforce full initialization of std::array

Question

I am using std::array (N is a fixed template-variable).

#include
template
struct A{
   size_t fun         


        

Answer 1

Simple answer: You cannot.

When initializing std::array with a list, it is doing an aggregate initialization, and it is explained here when the list size is less than the number of member:

• If the number of initializer clauses is less than the number of members or initializer list is completely empty, the remaining members are initialized by their brace-or-equal initializers, if provided in the class definition, and otherwise (since C++14) by empty lists, which performs value-initialization. If a member of a reference type is one of these remaining members, the program is ill-formed (references cannot be value-initialized)

It is simply a legal and acceptable behavior to provide less than the size list, so compiler will not complain anything. Your code:

A<5> a;
a.function({{1,2,3}}));

is equivalent to:

A<5> a;
a.function({{1,2,3,0,0}}));

to compiler. Your best bet is runtime error (which may not be as you wished).