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Re: Templated Casting operators

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Narinder wrote:

>>On Jul 8, 11:06 pm, Kai-Uwe Bux <jkherci...@gmx.net> wrote:
>>At the moment, I don't see why.
> 
> That is indeed curious.
> However on my issue, I think I am expecting something from C++ .. when
> I obviously should know better,  "C++ (101): C++ doesn't dispatch on
> the return type".

That, I think, is not the entire picture. There is clause [14.8.2.3] that 
deals with deducing template arguments for templated conversion operators. 
Here, the result type desired by the conversion is taken into account. 
Howerver, reading that clause, I find it hard to tell whether the deduction 
should fail because of ambiguity, whether the const version should be 
instantiated, or whether the non-const version should be chosen.

 
> My question stems from wanting to pass parameters to a function via an
> intermediary which holds references to the values to be passed. And
> this would be done at runtime.
> 
> Given :
> 
> void f( double x);
> 
> 
> I want to be able to do:
> 
> const double x=3.142;
> intermediary v = x; // so v will hold a
> std::tr1::reference_wrapper<const double>
> f(v);               // I suspect gcc will complain because v is unable
> to give up its const ref
>                     // but as we have seen gcc calls operator
> double&()

Hm, the following compiles:

#include <iostream>

void foo ( double arg ) {
  std::cout << arg << "\n";
}

  template < typename T >
  class reference_wrapper {

    T* the_ptr;

  public:

    typedef T type;
    typedef T& reference;
    
    reference_wrapper ( reference t_ref )
      : the_ptr ( &t_ref )
    {}

    operator reference ( void ) {
      return ( *the_ptr );
    }

    reference get ( void ) {
      return ( *the_ptr );
    }

 };

int main ( void ) {
  double const pi = 3.14159;
  reference_wrapper< double const > x = pi;
  foo( x );
}

> My way around this will be to have the user provide a precise boost
> typelist embodying the function signature:
> 
> boost::mpl::vector<double>
> 
> and use this to dispatch correctly.

Huh?


Best,

Kai-Uwe Bux

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Thread

Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-07 16:34 -0700
  Re: Templated Casting operators Alexander Bartolich <alexander.bartolich@gmx.at> - 2011-07-08 00:58 +0000
    Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-07 22:36 -0700
      Re: Templated Casting operators Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-07-08 09:42 +0200
        Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-08 01:16 -0700
          Re: Templated Casting operators Ian Collins <ian-news@hotmail.com> - 2011-07-08 20:23 +1200
        Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-08 01:37 -0700
          Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-08 06:28 -0700
        Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-08 01:40 -0700
          Re: Templated Casting operators Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-07-09 00:06 +0200
            Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-09 03:16 -0700
              Re: Templated Casting operators Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-07-09 13:34 +0200
                Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-09 07:18 -0700
                Re: Templated Casting operators Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-07-10 01:15 +0200
                Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-09 21:39 -0700
                Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-09 22:01 -0700
                Re: Templated Casting operators Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-07-10 13:43 +0200
                Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-10 05:55 -0700
                Re: Templated Casting operators Narinder <narinder.claire@gmail.com> - 2011-07-10 00:19 -0700
                Re: Templated Casting operators Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-07-10 12:03 +0200

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