This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

1726. Declarator operators and conversion function

[Accepted at the February, 2022 meeting.]

Presumably the following example is intended to be ill-formed:

  struct A {
    (*operator int*());
  };
  A a;
  int *x = a; // Ok?

It is not clear, however, which rule is supposed to reject such a member-declaration.

Proposed resolution (December, 2021):

Change 11.4.8.3 [class.conv.fct] paragraph 1 as follows, splitting the paragraph as indicated:

A member function of a class X with a name of the form

conversion-function-id:
operator conversion-type-id

conversion-type-id:
type-specifier-seq conversion-declarator_opt

conversion-declarator:
ptr-operator conversion-declarator_opt

A declaration whose declarator-id has an unqualified-id that is a conversion-function-id declares a conversion function; its declarator shall be a function declarator (9.3.4.6 [dcl.fct]) of the form

ptr-declarator ( parameter-declaration-clause ) cv-qualifier-seq_opt
ref-qualifier-seq_opt noexcept-specifier_opt attribute-specifier-seq_opt

where the ptr-declarator consists solely of an id-expression, an optional attribute-specifier-seq, and optional surrounding parentheses, and the id-expression has one of the following forms:

• in a member-declaration that belongs to the member-specification of a class or class template but is not a friend declaration (11.8.4 [class.friend]), the id-expression is a conversion-function-id;

• otherwise, the id-expression is a qualified-id whose unqualified-id is a conversion-function-id.

A conversion function shall have no parameters and shall be a non-static member function of a class or class template X; it specifies a conversion from X to the type specified by the conversion-type-id, interpreted as a type-id (9.3.2 [dcl.name]). Such functions are called conversion functions.

A decl-specifier in the decl-specifier-seq of a conversion function (if any) shall not be neither a defining-type-specifier nor static. The type of the conversion function (9.3.4.6 [dcl.fct]) is “noexcept_opt function taking no parameter cv-qualifier-seq_opt ref-qualifier_opt returning conversion-type-id”.

A conversion function is never used to convert a (possibly cv-qualified) object to the (possibly cv-qualified) same object type (or a reference to it), to a (possibly cv-qualified) base class of that type (or a reference to it), or to cv void.¹⁰² [Example 1:...