Re: reference don't work

From:

"Greg Herlihy" <greghe@pacbell.net>

Newsgroups:

comp.lang.c++.moderated

Date:

23 May 2006 17:50:07 -0400

Message-ID:

<1148400254.326320.300670@i39g2000cwa.googlegroups.com>

Bernhard Ibertsberger wrote:

Hi,

while playing around with a bind-implementation found in a well known
paper i got a compiler error in the marked line, which i can't explain.
Can anyone help me?

thx
Bernhard

// simple bind

template <typename R, typename T, typename Arg>
class simple_bind_t {
   typedef R (T::*fn)(Arg);
   fn fn_;
   T t_;
public:
   simple_bind_t(fn f, const T& t) :
     fn_(f),
     t_(t)
   {
   }
   R operator()(Arg& a) {
     return (t_.*fn_)(a);
   }
};

The problem is that operator() does not match the bound member function
signature exactly. The member function accepts a parameter of type Arg
- while operator() accepts a reference to type Arg. So in the case that
Arg is already a reference type - then operator()'s parameter would
have to be a reference to a reference type - which is not a legal type.
So whenever Arg is a reference type, operator() cannot be called.

The fix is to declare operator() so that its signature matches the
bound member function's signature exactly:

    R operator()(Arg a)
    {
        return (t_.*fn_)(a);
    }

Greg

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