CWG Issue 1608 (original) (raw)

This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 118e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-11-05

1608. Operator lookup in trailing return type

Section: 12.2.2.3 [over.match.oper]Status: C++14Submitter: Johannes SchaubDate: 2013-01-23

[Moved to DR at the September, 2013 meeting.]

There is an unfortunate disparity between the treatment of an example like

struct S { int operator; auto f() -> decltype(this->operator); };

(which is permitted, cf _N4567_.5.1.1 [expr.prim.general] paragraph 3), and

struct S { int operator; auto f() -> decltype((*this)[0]); };

which is not. The reason for rejecting the latter is 12.2.2.3 [over.match.oper] paragraph 3:

For a unary operator @ with an operand of a type whose cv-unqualified version is T1, and for a binary operator @with a left operand of a type whose cv-unqualified version is T1and a right operand of a type whose cv-unqualified version is T2, three sets of candidate functions, designated member candidates, non-member candidates and built-in candidates, are constructed as follows:

• If T1 is a complete class type, the set of member candidates is the result of the qualified lookup of T1::operator@(12.2.2.2.2 [over.call.func]); otherwise, the set of member candidates is empty.
• ...

It would be desirable to update the latter specification to allow lookup of preceding declarations in a class currently being defined, analogously with the lookup performed in the function-notation case.

Proposed resolution (April, 2013):

Change 12.2.2.3 [over.match.oper] bullet 3.1 as follows:

• If T1 is a complete class type or a class currently being defined, the set of member candidates is the result of the qualified lookup of T1::operator@ (12.2.2.2.2 [over.call.func]); otherwise, the set of member candidates is empty.