Initialisation of aggregate with default constructor deleted in c++20

Question

There is a struct containing POD and default constructor deleted. Trying to aggregate-initalize an instance of the struct results in compilation error in g++9.1 when compiled with -std=c++2a. The same code compiles fine with -std=c++17.

https://godbolt.org/z/xlRHLL

struct S
{
    int a;
    S() = delete;
};

int main()
{
    S s {.a = 0};
}

Answer 1

Your struct is not an aggregate since C++20.

The definition of aggregate was changed once again:

cppreference

An aggregate is one of the following types:

• ...

• class type (typically, struct or union), that has

  • ...

  • no user-provided, inherited, or explicit constructors (explicitly defaulted or deleted constructors are allowed)
    (since C++17) (until C++20)

  • no user-declared or inherited constructors
    (since C++20)

IMO, this fixes a defect in the language. Being able to construct (with aggregate initializaton) objects with deleted or inaccessible constructors doesn't look right to me.