This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2023-01-15


431. Defect in wording in 14.2

Section: 13.3  [temp.names]     Status: C++11     Submitter: Mat Marcus     Date: 10 August 2003

[Voted into WP at August, 2010 meeting.]

Consider this example:

   class Foo {
   public:
       template< typename T > T *get();
   };

   template< typename U >
   U *testFoo( Foo &foo ) {
       return foo.get< U >(); //#1
   }

I am under the impression that this should compile without requiring the insertion of the template keyword before get in the expression at //#1. This notion is supported by this note excerpted from 13.3 [temp.names]/5:

[Note: just as is the case with the typename prefix, the template prefix is allowed in cases where it is not strictly necessary; i.e., when the expression on the left of the -> or ., or the nested-name-specifier is not dependent on a template parameter.]

But 13.3 [temp.names]/4 contains this text:

When the name of a member template specialization appears after . or -> in a postfix-expression, or after nested-name-specifier in a qualified-id, and the postfix-expression or qualified-id explicitly depends on a template-parameter (14.6.2), the member template name must be prefixed by the keyword template. Otherwise the name is assumed to name a non-template.

The only way that I can read this to support my assumption above is if I assume that the phrase postfix-expression is used twice above with different meaning. That is I read the first use as referring to the full expression while the second use refers to the subexpression preceding the operator. Is this the correct determination of intent? I find this text confusing. Would it be an improvement if the second occurrence of "postfix-expression" should be replaced by "the subexpression preceding the operator". Of course that begs the question "where is subexpression actually defined in the standard?"

John Spicer: I agree that the code should work, and that we should tweak the wording.

Proposed resolution (March, 2010):

Change 13.3 [temp.names] paragraph 4 as follows:

When the name of a member template specialization appears after . or -> in a postfix-expression, or after a nested-name-specifier in a qualified-id, and the object or pointer expression of the postfix-expression or the nested-name-specifier in the qualified-id explicitly depends on a template-parameter template parameter (13.8.3 [temp.dep]) but does not refer to a member of the current instantiation (13.8.3.2 [temp.dep.type]), the member template name must be prefixed by the keyword template. Otherwise the name is assumed to name a non-template. [Example:...