Re: [boost] "Simple C++11 metaprogramming"

Subject: Re: [boost] "Simple C++11 metaprogramming"
From: Peter Dimov (lists_at_[hidden])
Date: 2015-06-02 10:08:24

Bruno Dutra wrote:

> What you mean? std::decay<>::type is the lazy backend.

Eh, no, it's just an implementation detail. Change your

template<> struct test_c<void>{using type = void;};

to

template<> struct test_c<int>{using type = int;};

and then look at the following decay<> of mine, which I'm sure you'll agree 
really has no "lazy backend".

template<class T> T make();
template<class T> T decay_impl(T);
template<class T> using decay = decltype(decay_impl(make<T&&>()));

template<class T> using test2 = test<decay<T>>;

static_assert(is_evaluable<test2, int const volatile>::value, "");
static_assert(!is_evaluable<test2, int()>::value, "");
static_assert(!is_evaluable<test2, void, int>::value, "");

is_evaluable still works as expected.

It even works on decay<> directly:

static_assert(is_evaluable<decay, int const volatile>::value, "");
static_assert(is_evaluable<decay, int()>::value, "");
static_assert(!is_evaluable<decay, int, float>::value, "");
static_assert(!is_evaluable<decay, void>::value, "");