[cfe-dev] a question on __invoke

[苏焕然]

Thank you for your reply!
And after reading the whole std::bind implementation, I've realized that
std::bind could take pointer to object as well as shared_ptr/unique_ptr as
it's input.


On Fri, Jul 11, 2014 at 12:12 AM, Marshall Clow <mclow.lists at gmail.com>
wrote:

>
> On Jul 9, 2014, at 3:41 AM, 苏焕然 <ownesss at gmail.com> wrote:
>
> I don't quite understand about __invoke bullet2 and bullet4.
>
> for example, bullet2:
>
> template <class _Fp, class _A0, class ..._Args,
>>  class = typename enable_if
>>  <
>> is_member_function_pointer<typename remove_reference<_Fp>::type>::value
>> &&
>>  !is_base_of<typename remove_reference<typename __member_pointer_traits<
>> typename remove_reference<_Fp>::type>::_ClassType>::type,
>>  typename remove_reference<_A0>::type>::value
>>  >::type
>> >
>> _LIBCPP_INLINE_VISIBILITY
>> auto
>> __invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
>>  -> decltype(((*_VSTD::forward<_A0>(__a0)).*__f)(_VSTD::forward<_Args>(
>> __args)...));
>
>
> this functions invokes *f* with *(*a0).f(args) (*as written in header
> __functional_base)*, *so I guess that a0/A0 has the type of *Pointer to
> Class? (thus, of course, isn't a base class of himself)*
>
> Then why did *enable_if *just test if *ClassType* of *f *isn't a base
> class of *A0 *?
> wouldn't
>
>     && is_base_of<member_pointer_traits<_Fp>::ClassType,
>> remove_pointer<A0>>::value
>
>
> be more accurate? also, wouldn't <Some_Class_C::*Fp, Some_Class_D,
> Some_Args...> makes the value of enable_if to be true?
>
> I must guess that there is something I hadn't taken into consideration ;>
>
>
> The enable_if conditions are taken directly from the description in the
> standard (using N3936 here), 20.9.2/1:
>
> Define INVOKE (f, t1, t2, ..., tN) as follows:
>
> — (t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class
> T and t1 is an object of
> type T or a reference to an object of type T or a reference to an object
> of a type derived from T;
>
> — ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
> class T and t1 is not one of
> the types described in the previous item;
>
> — Bullet #3 elided
> — Bullet #4 elided
> — Bullet #5 elided
>
> — Marshall
>
>
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