Why ={} initialization doesn't work for tuple?

Question

To me a pair is just special case of a tuple, but following surprises me:

pair p1(1, 2);   // ok
tuple

        

Answer 1

In addition to Praetorian's correct answer (which I've upvoted), I wanted to add a little more information...

Post-C++14, the standard has been changed to allow:

tuple<int, int> t2={1, 2}; 

to compile and have the expected semantics. The proposal that does this is N4387. This will also allow constructs such as:

tuple<int, int>
foo()
{
    return {1, 2};
}

It only allows it if all T in the tuple are implicitly contructible from all arguments.

As a non-conforming extension, libc++ already implements this behavior.

Answer 2

The tuple constructor you're trying to call is explicit, so copy-list-initialization will fail. The corresponding pair constructor is not explicit.

Change your code to

tuple<int, int> t2{1, 2};

and it'll compile.