RE: c++/10273: g++ fails to compile sort() with a template operatorthat takes a pointer

[Wolfgang Bangerth <bangerth at ices dot utexas dot edu>]

The following reply was made to PR c++/10273; it has been noted by GNATS.

From: Wolfgang Bangerth <bangerth at ices dot utexas dot edu>
To: "Darren Reed (OSE)" <darrenr at optimation dot com dot au>
Cc: gcc-bugs at gcc dot gnu dot org, <gcc-gnats at gcc dot gnu dot org>
Subject: RE: c++/10273: g++ fails to compile sort() with a template operator
 that takes a pointer
Date: Mon, 31 Mar 2003 17:31:12 -0600 (CST)

 > Is it unreasonable to ask for a better error message in this case ?
 > Or perhaps better checking of templates ?  (This would probably cause
 > a more accurate error message to be output.)
 
 I guess in this case, the error message is as clear as it can be: the 
 declaration of the template is legal (you parameterize it on a value, not 
 on a type as you had expected) so there is nothing the compiler could have 
 told you there. Then you tried to use the template with a type instead of 
 the required value and the compiler told you
   x.cc: In function `void std::doit()':
   x.cc:31: type/value mismatch at argument 1 in template parameter list for `
    template<std::ClassName*<anonymous> > struct std::xLess'
   x.cc:31:   expected a constant of type `std::ClassName*', got `std::ClassName*'
 
 I think the message says it quite clearly: first the type/value mismatch, 
 then in addition that it expected a value and got a type. What more do you 
 want?
 
 Regards
   Wolfgang
 
 PS: General experience from such mishaps is a) don't use existing names 
 for template parameters (you re-used ClassName, which is an existing class 
 name, as the name of the template parameter), and b) use "typename" 
 instead of "class" in template argument lists. Both measures would have 
 yielded the syntax error that you expected at the point of declaration of 
 the template.
 
 -------------------------------------------------------------------------
 Wolfgang Bangerth             email:            bangerth at ticam dot utexas dot edu
                               www: http://www.ticam.utexas.edu/~bangerth/