////
Copyright 2017 Peter Dimov

Distributed under the Boost Software License, Version 1.0.

See accompanying file LICENSE_1_0.txt or copy at
http://www.boost.org/LICENSE_1_0.txt
////

[#function]
# Helper Metafunctions, <boost/mp11/function.hpp>
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## mp_void<T...>

    template<class... T> using mp_void = void;

Same as `std::void_t` from C++17.

## mp_and<T...>

    template<class... T> using mp_and = /*...*/;

`mp_and<T...>` applies `mp_to_bool` to the types in `T...`, in order. If the result of an application is `mp_false`, `mp_and`
returns `mp_false`. If the application causes a substitution failure, returns `mp_false`. If all results are `mp_true`,
returns `mp_true`. `mp_and<>` is `mp_true`.

    using R1 = mp_and<mp_true, mp_true>;   // mp_true
    using R2 = mp_and<mp_false, void>;     // mp_false, void is not reached
    using R3 = mp_and<mp_false, mp_false>; // mp_false
    using R4 = mp_and<void, mp_true>;      // mp_false (!)

## mp_all<T...>

    template<class... T> using mp_all = /*...*/;

`mp_all<T...>` is `mp_true` if `mp_to_bool<U>` is `mp_true` for all types `U` in `T...`, `mp_false` otherwise. Same as
`mp_and`, but does not perform short-circuit evaluation. `mp_and<mp_false, void>` is `mp_false`, but `mp_all<mp_false, void>`
is an error because `void` does not have a nested `value`. The upside is that `mp_all` is potentially faster and does not
mask substitution failures as `mp_and` does.

    using R1 = mp_and<mp_true, mp_true>;   // mp_true
    using R2 = mp_and<mp_false, void>;     // compile-time error
    using R3 = mp_and<mp_false, mp_false>; // mp_false
    using R4 = mp_and<void, mp_true>;      // compile-time error

## mp_or<T...>

    template<class... T> using mp_or = /*...*/;

`mp_or<T...>` applies `mp_to_bool` to the types in `T...`, in order. If the result of an application is `mp_true`, `mp_or`
returns `mp_true`. If all results are `mp_false`, returns `mp_false`. `mp_or<>` is `mp_false`.

    using R1 = mp_or<mp_true, mp_false>;   // mp_true
    using R2 = mp_or<mp_true, void>;       // mp_true, void is not reached
    using R3 = mp_or<mp_false, mp_false>;  // mp_false
    using R4 = mp_or<void, mp_true>;       // compile-time error

## mp_any<T...>

    template<class... T> using mp_any = /*...*/;

`mp_any<T...>` is `mp_true` if `mp_to_bool<U>` is `mp_true` for any type `U` in `T...`, `mp_false` otherwise. Same as
`mp_or`, but does not perform short-circuit evaluation.

    using R1 = mp_any<mp_true, mp_false>;  // mp_true
    using R2 = mp_any<mp_true, void>;      // compile-time error
    using R3 = mp_any<mp_false, mp_false>; // mp_false
    using R4 = mp_any<void, mp_true>;      // compile-time error

## mp_same<T...>

    template<class... T> using mp_same = /*...*/;

`mp_same<T...>` is `mp_true` if all the types in `T...` are the same type, `mp_false` otherwise. `mp_same<>` is `mp_true`.

## mp_plus<T...>

    template<class... T> using mp_plus = /*...*/;

`mp_plus<T...>` is an integral constant type with a value that is the sum of `U::value` for all types `U` in `T...`.
`mp_plus<>` is `mp_int<0>`.
