Aggregate initialization of non-POD class types?

Question

Is it legal to aggregate initialize non-POD class types in ISO C++?

For example if we have a structure with a single method like this:

struct T
{
   operator double();

   int a;

   int b;
} ;

And we initialize an instance of it:

T tObj { 56, 92 };

using aggregate initialization. Is this legal?

Under Clang 3.7 it compiles fine although in VC++ 15 CTP 3 it doesn't.

Any insights on the question and a quote from the standard please?

That it can find a suitable constructor to call or something. — AnArrayOfFunctions, Mar 04 '15 at 16:22
Your class is an aggregate so aggregate initialization is fine. Your class is even POD, but that is irrelevant here. — juanchopanza, Mar 04 '15 at 16:23
Are you perhaps using in class member intializers? Which would make it a [non-aggregate in C++11](http://stackoverflow.com/q/27118535/1708801) , the error makes more sense in that case. — Shafik Yaghmour, Mar 04 '15 at 16:25

Mike Seymour · Accepted Answer · 2015-03-04T16:27:39.557

You can aggregate-initialise any aggregate, whether or not it's POD. C++11 defines an aggregate thusly:

[dcl.init.aggr] An aggregate is an array or a class with no user-provided constructors, no brace-or-equal-initializers for non-static data members, no private or protected non-static data members, no base classes, and no virtual functions

and your class meets that description.

C++14 relaxes the restrictions on aggregates, removing "no brace-or-equal-initializers for non-static data members"; that doesn't affect this question.

Note that your class is also POD; simply having a member function doesn't disqualify it. But being POD is largely unrelated to whether or not it's an aggregate.

Aggregate initialization of non-POD class types?

1 Answers1