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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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