c++/8567: std::endl is of unknown type when overloading operator<< (repeat in case attachment didnt work)

[Jason Stanek]

The following reply was made to PR c++/8567; it has been noted by GNATS.

From: Jason Stanek <jstanek@iastate.edu>
To: bangerth@dealii.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
        jstanek@iastate.edu, jstanek@vrac.iastate.edu, nobody@gcc.gnu.org,
        gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: c++/8567: std::endl is of unknown type when overloading
  operator<< (repeat in case attachment didnt work)
Date: Thu, 14 Nov 2002 21:13:20 -0600

 Isnt there a way to specify a default template type?
 
 So instead of declaring endl as a pure template, it has a default type in 
 the case that you dont specify one.
 
 Something like this:
 
 namespace std {
        template <typename T=int> T& endl (T&);
 };
 
 -Jason
 
 At 11:37 PM 11/14/2002 +0000, you wrote:
 >Synopsis: std::endl is of unknown type when overloading operator<< (repeat 
 >in case attachment didnt work)
 >
 >State-Changed-From-To: open->closed
 >State-Changed-By: bangerth
 >State-Changed-When: Thu Nov 14 15:37:17 2002
 >State-Changed-Why:
 >     Not a bug. Basically, it is this:
 >     ---------------------------------
 >     namespace std {
 >       template <typename T> T& endl (T&);
 >     };
 >
 >     class BlackHole{};
 >
 >     template <typename T> BlackHole& operator<<(BlackHole& bh, const T& 
 > dummy);
 >     template <typename T> BlackHole& operator<<(BlackHole& bh, T& 
 > (*dummy)(T&));
 >
 >     int main() {
 >       BlackHole bh;
 >       bh << std::endl;
 >     }
 >     -------------------------------
 >     Since there is no unambiguous function std::endl, the
 >     compiler cannot know which one to take as argument, so
 >     you have to disambiguate the situation by passing it the
 >     exact template argument list. Alternatively, you can give
 >     an overloaded non-template op<<; in this example, this
 >     would do:
 >       BlackHole& operator<<(BlackHole& bh, int& (*dummy)(int&));
 >     Then std::endl<int> would be taken.
 >
 >     W.
 >
 >http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8567