Re: Help with templates and code generalization

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Mon, 14 May 2007 10:41:33 -0400

Message-ID:

<f29sf1$p9l$1@news.datemas.de>

StephQ wrote:

Sorry for the very late reply.
I have big problems in trying to get code that uses mem_fun1 to work.
Here below is a very simplifyed example:

#include <iostream>
#include <functional>

using namespace std;

template<typename F>
class Display {
public:
   static void computePlot(std::ostream& ss, F f)
   {
   ss << f( 1.0 ) << endl;
   }
};

template<class F>
void plot(std::ostream& os, F f) {
   return Display<F>::computePlot(os, f);
}

class Doubler {
public:
   double foo(double x) const { return 2*x; }

Drop the 'const'.

};

int main() {
plot(cout, mem_fun1(&Doubler::foo));

Change to

Doubler d;
plot(cout, bind1st(mem_fun1(&Doubler::foo), &d));

Otherwise you're trying to make the program call a non-static member
function without an instance.

}

The error I'm getting is:
no instance of function template "std::mem_fun1" matches the argument
list
argument types are: (double (Doubler::*)(double) const)
plot(cout, mem_fun1(&Doubler::foo));

If I remove the const keyword from foo I still get the following
error:

error: no instance of function "std::mem_fun1_t<_Result, _Ty,
_Arg>::operator() [with _Result=double, _Ty=Doubler, _Arg=double]"
matches the argument list
argument types are: (double)
object type is: std::mem_fun1_t<double, Doubler, double>
ss << f( 1.0 ) << endl;
^
detected during:
instantiation of "void Display<F>::computePlot(std::ostream &, F)
[with F=std::mem_fun1_t<double, Doubler, double>]" at line 19
instantiation of "void plot(std::ostream &, F) [with
F=std::mem_fun1_t<double, Doubler, double>]"

V
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