Why does inheriting constructors break aggregate initialization? [duplicate]

Question

Why does inheriting constructors from a base class break aggregate initialization?

For example, this works:

struct MyArray : std::array<int, 2ul> {};

MyArray a{1, 2};

but this doesn't work:

struct MyArray : std::array<int, 2ul>
{
     using std::array<int, 2ul>::array;
};

MyArray a{1, 2};

Answer 1

Since C++17, aggregates can have base classes, so that for such structures being derived from other classes/structures list initialization is allowed:

struct MoreData : Data {
    bool done;
};

MoreData y{{"test1", 6.778}, false};

In C++17 an aggregate is defined as

• either an array
• or a class type (class, struct, or union) with:
  • no user-declared or explicit constructor
  • no constructor inherited by a using declaration
  • no private or protected non-static data members
  • no virtual functions
  • no virtual, private, or protected base classes

For more details you can refer to Chapter 4 Aggregate Extensions from C++17 - The Complete Guide By Nicolai M. Josuttis