Re: [boost] Another C++ puzzler

From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-04-27 10:22:48

AMDG

Marco Costalba wrote:
> To disambiguate between the two a SFINAE technique is used on the
> second (hidden) argument of "set"
>
> Where struct is_compatible is defined as:
>
>
>    /* Check if a function/functor Fun has a given signature Sig */
>
>     template<typename Fun, typename Sig>
>     struct is_compatible
>     {
>         /* Check for a function */
>         template<class U> static
>         yes_type check(typename enable_if<is_same<U, Sig> >::type*);
>
>         /* Check for a functor */
>         template<class U, Sig U::*> struct helper;
>
>         template<class U> static
>         yes_type check(helper<U, &U::operator()>*);
>   

This is not correct.  It does not handle

struct f {
    void operator()() *const* {}
};

Further, it cannot handle implicit conversions of the argument types
and return types.

>         /* Default */
>         template<class U> static no_type check(...);
>
>         typedef typename boost::remove_pointer<Fun>::type F;
>
>         static bool const value = (sizeof(check<F>(0)) == sizeof(yes_type));
>     };
>
>   

In Christ,
Steven Watanabe