C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Defect Report: Incorrect narrative in the Template Parameter          C++Talk.NET Forum Index -> C++ language, library and standards View previous topic :: View next topic   Author Message Andre Morozov Guest Posted: Fri Dec 16, 2005 3:45 pm    Post subject: Defect Report: Incorrect narrative in the Template Parameter [ Note: forwarded to C++ committee. -sdc ] The text of the draft [N1905=05-0165], clause 2, states that the word typename followed by a qualified-id denotes the type of a non-type parameter declaration: ------------------------------------------------------------------------------------------ 14.1 Template parameters [temp.param] 1 The syntax for template-parameters is: template-parameter: type-parameter parameter-declaration ... 2 There is no semantic difference between class and typename in a template-parameter. typename followed by an unqualified-id names a template type parameter. *** typename followed by a qualified-id denotes the type in a non-type 132) parameter-declaration. *** ------------------------------------------------------------------------------------------- However, qualified-id is defined as a sequence that either begins with :: or nested-name-specifier, which is always followed by ::. The text should probably say "typename followed by decl-specifier-seq denotes the type in a non-type parameter-declaration". Regards, Andre Morozov [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top william.m.miller@gmail.co Guest Posted: Fri Dec 23, 2005 5:57 am    Post subject: Re: Defect Report: Incorrect narrative in the Template Param Andre Morozov wrote: Quote: The text of the draft [N1905=05-0165], clause 2, states that the word typename followed by a qualified-id denotes the type of a non-type parameter declaration: ------------------------------------------------------------------------------------------ 14.1 Template parameters [temp.param] 1 The syntax for template-parameters is: template-parameter: type-parameter parameter-declaration .. 2 There is no semantic difference between class and typename in a template-parameter. typename followed by an unqualified-id names a template type parameter. *** typename followed by a qualified-id denotes the type in a non-type 132) parameter-declaration. *** ------------------------------------------------------------------------------------------- However, qualified-id is defined as a sequence that either begins with :: or nested-name-specifier, which is always followed by ::. The text should probably say "typename followed by decl-specifier-seq denotes the type in a non-type parameter-declaration". No, this says what it says intentionally. The issue is that there is an apparent ambiguity between use of the "typename" keyword to declare a template type parameter and its use to mark a dependent name as a type (14.6p3). The latter use can only occur with a qualified-id, so use of typename with an unqualified-id is always a declaration of a template type parameter, regardless of whether the identifier is a type-name in the containing scope. For example: struct T { }; template <typename T> void f(T); The "T"s in the declaration of "f" are both a template type parameter and not the class-name ::T. (Cf 14.1p3.) On the other hand, in a declaration like template <typename T> struct X; template <typename T, typename X void g(T); the second template parameter in the declaration of "g" is an unnamed non-type parameter; the "typename" keyword identifies X<T>::type as a type. I agree that the description in 14.1p2 is not as clear as it should be, however, so I will open a core language issue suggesting a clarification. -- William M. (Mike) Miller Edison Design Group --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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