Re: [boost] enable_if and non-template member functions?

Subject: Re: [boost] enable_if and non-template member functions?
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2011-08-12 17:14:24

On Fri, 12 Aug 2011, Mostafa wrote:

> On Fri, 12 Aug 2011 02:31:10 -0700, John Maddock <boost.regex_at_[hidden]> 
> wrote:
>
>>> From your description, I think I've done exactly this.  E.g.
>> 
>> --8<---------------cut here---------------start------------->8---
>> template <class U>
>> struct X
>> {
>>     // member function void f(int) becomes something like:
>>     template <class T>
>>     typename enable_if<
>>        mpl::and_<
>>            is_convertible<T,int>
>>          , some_condition_on<U>
>>        >
>>     >::type
>>     f(T x_)
>>     { int x = x_; ... }
>> };
>> --8<---------------cut here---------------end--------------->8---
>> 
>> That works as long as the function has at least one parameter that can be 
>> turned into a template, but I have some cases that are operators or else 
>> have no parameters.
>
> In case of no-parameter functions or operators, what's wrong with:
>
> template <class U>
> struct T
> {
>   void f()
>   {
>       f_impl(<static_cast<void *>(0));
>   }
>
> private:
>   template <class T>
>   typename enable_if<
>       mpl::and_<
>       is_convertible<T, void *>,
>       some_condition_on<U>
>    >::type
>    f_impl(T)
>    { .... }
> };

In that case, f would not be covered by SFINAE, since it is not a 
template.  Calls to f would fail because of the lack of f_impl, but that 
would be done after overload resolution.

-- Jeremiah Willcock