Can Classes with Non-Static Member Initializers Be Aggregates in C 14?

C 11 Aggregate Initialization for Classes with Non-Static Member Initializers

In C 11, structures and classes with user-defined constructors and private or protected non-static data members are not considered aggregates. Historically, this was also the case for classes with non-static member initializers, even though they lacked user-defined constructors.

However, in C 14, this restriction was removed. Now, classes with non-static member initializers can still be aggregates, as long as they meet the other requirements for aggregates:

• No user-defined constructors
• No private or protected non-static data members
• No base classes
• No virtual functions

For example:

struct A
{
  int a = 3;
  int b = 3;
};

int main()
{
  A a{0, 1}; // This is now allowed in C++14
  return 0;
}

This change was motivated by the desire to align the behavior of aggregate initialization with intuition. In-class initializers are essentially equivalent to user-defined constructors, but it is counterintuitive for them to prevent a class from being an aggregate.

Since G 5.0, C 14 aggregates with non-static data member initializers have been supported using std=c 1y or -std=c 14.

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