Re: [boost] Interesting variadic template trick

Subject: Re: [boost] Interesting variadic template trick
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2013-11-18 01:54:31

On Mon, Nov 18, 2013 at 10:18 AM, Steven Watanabe <watanabesj_at_[hidden]> wrote:
> AMDG
>
> On 11/17/2013 09:55 PM, Andrey Semashev wrote:
>>
>>>     template <typename ...T>
>>>     struct or_ {
>>>         static constexpr bool value = !all_pointers(
>>>             ((typename std::conditional<T::value, int, void*>::type)0)...
>>>         );
>>>     };
>>>
>>>     template <>
>>>     struct or_<> {
>>>         static constexpr bool value = false;
>>>     };
>>
>>
>> It requires N instantiations of std::conditional, doesn't it? In that
>> case is it actually faster than the naive recursive instantiation of
>> or_?
>>
>
> No it doesn't.  It requires exactly two
> instantiations of std::conditional for
> all uses of or_.

You mean the compiler can optimize multiple instantiations for
different T::value values to just unique ones?