forked from boostorg/mp11
94 lines
2.9 KiB
Plaintext
94 lines
2.9 KiB
Plaintext
////
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Copyright 2017 Peter Dimov
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Distributed under the Boost Software License, Version 1.0.
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See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt
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////
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[#utility]
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# Utility Components, <boost/mp11/utility.hpp>
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:toc:
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:toc-title:
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:idprefix:
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## mp_identity<T>
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template<class T> struct mp_identity
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{
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using type = T;
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};
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## mp_identity_t<T>
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template<class T> using mp_identity_t = T;
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## mp_inherit<T...>
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template<class... T> struct mp_inherit: T... {};
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## mp_if_c<C, T, E...>
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template<bool C, class T, class... E> using mp_if_c = /*...*/;
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`mp_if_c<true, T, E...>` is an alias for `T`. `mp_if_c<false, T, E>` is an alias for `E`. Otherwise, the result is a substitution failure.
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using R1 = mp_if_c<true, int, void>; // int
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using R2 = mp_if_c<flase, int, void>; // void
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template<class I> using void_if_5 = mp_if_c<I::value == 5, void>; // `void` when `I::value` is 5, substitution failure otherwise
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## mp_if<C, T, E...>
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template<class C, class T, class E...> using mp_if = mp_if_c<static_cast<bool>(C::value), T, E...>;
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Like `mp_if_c`, but the first argument is a type.
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## mp_eval_if_c<C, T, F, U...>
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template<bool C, class T, template<class...> class F, class... U> using mp_eval_if_c = /*...*/;
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`mp_eval_if_c<C, T, F, U...>` is an alias for `T` when `C` is `true`, for `F<U...>` otherwise. Its purpose
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is to avoid evaluating `F<U...>` when the condition is `true` as it may not be valid in this case.
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## mp_eval_if<C, T, F, U...>
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template<class C, class T, template<class...> class F, class... U> using mp_eval_if = mp_eval_if_c<static_cast<bool>(C::value), T, F, U...>;
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Like `mp_eval_if_c`, but the first argument is a type.
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## mp_eval_if_q<C, T, Q, U...>
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template<class C, class T, class Q, class... U> using mp_eval_if_q = mp_eval_if<C, T, Q::template fn, U...>;
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Like `mp_eval_if`, but takes a quoted metafunction.
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## mp_valid<F, T...>
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template<template<class...> class F, class... T> using mp_valid = /*...*/;
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`mp_valid<F, T...>` is an alias for `mp_true` when `F<T...>` is a valid expression, for `mp_false` otherwise.
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## mp_defer<F, T...>
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template<template<class...> class F, class... T> using mp_defer = /*...*/;
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When `mp_valid<F, T...>` is `mp_true`, `mp_defer<F, T...>` is a struct with a nested type `type` which is an alias for `F<T...>`. Otherwise,
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`mp_defer<F, T...>` is an empty struct.
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## mp_quote<F>
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template<template<class...> class F> struct mp_quote
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{
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template<class... T> using fn = F<T...>;
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};
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`mp_quote<F>` transforms the template `F` into a type with a nested template `fn` such that `fn<T...>` returns `F<T...>`.
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## mp_invoke<Q, T...>
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template<class Q, class... T> using mp_invoke = typename Q::template fn<T...>;
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`mp_invoke<Q, T...>` evaluates the nested template `fn` of a quoted metafunction. `mp_invoke<mp_quote<F>, T...>` returns `F<T...>`.
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