Proposed resolution:

This wording is relative to N4762.

• Edit [atomics.ref.generic], class template atomic_ref synopsis, as indicated:

  […]
  atomic_ref() = delete;
  atomic_ref& operator=(const atomic_ref&) = delete;
  […]
  

• Edit [atomics.ref.int], class template specialization atomic_ref<integral> synopsis, as indicated:

  […]
  atomic_ref() = delete;
  atomic_ref& operator=(const atomic_ref&) = delete;
  […]
  

• Edit [atomics.ref.float], class template specialization atomic_ref<floating-point> synopsis, as indicated:

  […]
  atomic_ref() = delete;
  atomic_ref& operator=(const atomic_ref&) = delete;
  […]
  

• Edit [atomics.ref.pointer], class template specialization atomic_ref<T*> synopsis, as indicated:

  […]
  atomic_ref() = delete;
  atomic_ref& operator=(const atomic_ref&) = delete;
  […]
  

[ 2018-11, Adopted in San Diego ]

[ 2018-10-06 Status to Tentatively Ready after seven positive votes on the reflector. ]

atomic_ref has a deleted default constructor, which causes pointless ambiguities in cases like:

void meow(atomic_ref<int>);
void meow(some_default_constructible_struct);

meow({});

It should have no default constructor rather than a deleted one. (Note that it has other user-defined constructors and so cannot be an aggregate under any definition.)