Re: [Boost-users] enable_if for class members

Subject: Re: [Boost-users] enable_if for class members
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2009-01-30 12:44:21

On Fri, Jan 30, 2009 at 6:21 AM, Christopher Jefferson
<chris_at_[hidden]> wrote:
> In a class, I want to have one member function which has different
> implementations depending on one of the template parameters. I tried to use
> enable_if
>
> template<bool b>
> struct foo
> {
>  typename boost::enable_if_c<b, int>::type
>  get_val( )
>  { return 2; }
>
>  typename boost::disable_if_c<b, int>::type
>  get_val()
>  { return 3; }
> };
>
> But when I use foo in code, it doesn't work, complaning that:
>  error: no type named 'type' in 'struct boost::enable_if_c<true, int>'
>
> Am I not using enable_if in the correct way? Is there any easy way to do
> waht I'm trying to do? I used to do this by declaring an inner class and
> overloading that, but then it is necessary to pass in the class and the code
> looks very messy.

You could specialize the member function:

template<bool>
struct foo
{
  int get_val();
};

template <>
int foo<false>::get_val()
{
  return 2;
}

template <>
int foo<true>::get_val()
{
  return 3;
}

Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode