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Document mp_cond

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Peter Dimov
2017-10-14 16:20:36 +03:00
parent 30fcc21d8b
commit 8f1aaa3b52
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doc/mp11/utility.adoc
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@ -22,7 +22,7 @@ http://www.boost.org/LICENSE_1_0.txt
`mp_identity` is a simple _transformation type trait_ (as per the C++ standard)
that just returns the same type. It's useful both as such, and as a type wrapper
useful for passing types as values to functions.
for passing types as values to functions.
.Using mp_identity as a type trait
```
@ -135,6 +135,27 @@ template<class L> using first_or_void = mp_eval_if<mp_empty<L>, void, mp_first,
Like `mp_eval_if`, but takes a quoted metafunction.
## mp_cond<C, T, R...>
template<class C, class T, class... R> using mp_cond = /*...*/;
`mp_cond<C, T, R...>` is an alias for `T` when `static_cast<bool>(C::value)` is `true`.
When `static_cast<bool>(C::value)` is `false`, it's an alias for `mp_cond<R...>`.
(If `static_cast<bool>(C::value)` is a substitution failure, the result is too a substitution
failure.)
.Using mp_cond
```
template<int N> using unsigned_ = mp_cond<
mp_bool<N == 8>, uint8_t,
mp_bool<N == 16>, uint16_t,
mp_bool<N == 32>, uint32_t,
mp_bool<N == 64>, uint64_t,
mp_true, unsigned // default case
>;
```
## mp_valid<F, T...>
template<template<class...> class F, class... T> using mp_valid = /*...*/;