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[/
Copyright 2018 Glen Joseph Fernandes
(glenjofe@gmail.com)
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).
]
[section:detected detected]
template<template<class...> class Op, class... Args>
using detected_t = __below;
__alias `Op<Args...>` if it is a valid template-id, otherwise
`boost::nonesuch`.
__std_paper [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4502.pdf N4502]
__compat Requires C++11 variadic templates and C++11 template aliases.
__header `#include <boost/type_traits/detected.hpp>`
__examples
Suppose you wish to determine whether a type has a `size()` const-member function, then given the meta-functions:
template <class T>
using size_member_tester = decltype(std::declval<const T&>().size());
template <class T>
using size_member_t = boost::detected_t<size_member_tester, T >;
Then the type `size_member_t<T>` is an alias for `size_member_tester<T>` if the operation is valid, and an alias for
`boost::nonesuch` otherwise.
See also: __is_detected, __is_detected_convertible, __is_detected_exact.
[endsect]
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