Re: c++/4205: function template can call other function with incorrect parameters

[Wolfgang Bangerth <bangerth@ticam.utexas.edu>]

The following reply was made to PR c++/4205; it has been noted by GNATS.

From: Wolfgang Bangerth <bangerth@ticam.utexas.edu>
To: gcc-bugs@gcc.gnu.org, <gcc-gnats@gcc.gnu.org>, <nathan@codesourcery.com>,
   <gdr@codesourcery.com>
Cc:  
Subject: Re: c++/4205: function template can call other function with incorrect
 parameters
Date: Fri, 15 Nov 2002 19:55:02 -0600 (CST)

 This code compiles silently:
 -------------------------------------
 template<typename F> void quirk(F f) {
   (*f) (1);
 }
 
 void foo(int i, int j = 5){}
 void bar(int i, int j)    {}
 
 int main() {
   quirk(&foo); 
   quirk(&bar);
 }
 -------------------------------------
 
 The assertion of the submitter is that the first quirk(&foo) is ok, since 
 the call to (*f)(1) will substitute the second arg of foo by the default 
 argument of that function. The second call would be wrong. It succeeds, of 
 course, since the function quirk for exactly this template arg has already 
 been compiled, and no re-compilation means no re-check.
 
 However, I believe that already the first one is bogus. The template 
 argument F of quirk is 
   void (*) (int, int),
 so the call to (*p)(1) should be invalid. We should not know about default 
 arguments in quirk, right? I'm surprised that default arguments are 
 propagated to the template function. They don't appear in the type of 
 quirk as well, since if I enter a
     std::cout << __PRETTY_FUNCTION__ << std::endl;
 into that function, I only get 
     void quirk(F) [with F = void (*)(int, int)]
 But that may of course have other roots.
 
 Regards
   Wolfgang
 
 -------------------------------------------------------------------------
 Wolfgang Bangerth              email:           bangerth@ticam.utexas.edu
                                www: http://www.ticam.utexas.edu/~bangerth