This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-04-13
[Voted into the WP at the March, 2011 meeting as part of paper N3282.]
Consider the following example:
struct vector { struct iterator { }; struct const_iterator { }; iterator begin(); const_iterator begin() const; }; class block { vector v; auto end() const -> decltype(v.begin()) { return v.begin(); } };Because the transformation of a member name into a class memberaccess expression (11.4.3 [class.mfct.non.static] paragraph 3) onlyoccurs inside the body of a non-static member function, the typeofv in thetrailing-return-type is non-const butis const in the return expression, resulting in a type mismatchbetween the return expression and the return type of the function.
One possibility would be to include thetrailing-return-typeas being subject to the transformation in 11.4.3 [class.mfct.non.static].Note, however, thatthis is currently not in scope at thatpoint (seeissue 945).
Notes from the November, 2010 meeting:
The CWG felt that, becausethis is effectively animplicit parameter, the best approach would be to model its usabilityon the visibility of parameters: it could be named wherever aparameter of the function is in scope.
Proposed resolution (February, 2011):
Change _N4567_.5.1.1 [expr.prim.general] paragraph 2 as follows,adding three new paragraphs:
The keywordthis names a pointer to the object for which anon-static member function (_N4868_.11.4.3.2 [class.this]) is invoked ora non-static data member's initializer (11.4 [class.mem]) isevaluated.
The keywordthis shall be used only inside thebody of a non-static member function (11.4.2 [class.mfct]) of thenearest enclosing class or in abrace-or-equal-initializer fora non-static data member (11.4 [class.mem]). The type of theexpression is a pointer to the class of the function or non-staticdata member, possibly with cv-qualifiers on the class type. Theexpression is a prvalue.If afunction-definition ormember-declaratordeclares a member function of a classX, the expressionthis is a prvalue of type “pointer tocv-qualifier-seqX” between the optionalcv-qualifier-seq and the end of thefunction-definitionormember-declarator. It shall not appear before the optionalcv-qualifier-seq and it shall not appear within the declarationof a static member function (although its type and value category isdefined within a static member function as it is within a non-staticmember function). [Note: the type and value category is definedeven for the case of a static member function because declarationmatching does not occur until the complete declarator is known, andthis may be used in thetrailing-return-type of thedeclarator. —end note]
Otherwise, if amember-declarator declares anon-static data member (11.4 [class.mem]) of a classX,the expressionthis is a prvalue of type “pointer toX” within the optionalbrace-or-equal-initializer.It shall not appear elsewhere in themember-declarator.
The expressionthis shall not appear in any othercontext.
[Example:...
Change _N4567_.5.1.1 [expr.prim.general] paragraph 10 as follows:
Anid-expression that denotes a non-static data member ornon-static member function of a class can only be used:
...
in the body ofbeyond the optionalcv-qualifier-seq in themember-declarator orfunction-definition that declares a non-static memberfunction of that class or of a class derived from that class(11.4.3 [class.mfct.non.static]), or...
Change 11.4.3 [class.mfct.non.static] paragraph 3 as follows:
When anid-expression (7.5 [expr.prim]) that is notpart of a class member access syntax (7.6.1.5 [expr.ref]) andnot used to form a pointer to member (7.6.2.2 [expr.unary.op]) isused in thebodydeclaration of anon-staticmember function of classX, if namelookup (6.5 [basic.lookup]) resolves the name...