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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:is_detected is_detected]
- template<template<class...> class Op, class... Args>
- using is_detected = __below;
- template<template<class...> class Op, class... Args>
- constexpr bool is_detected_v = is_detected<Op, Args...>::value;
- __alias If `Op<Args...>` is a valid template-id, aliases __true_type,
- otherwise aliases __false_type.
- __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/is_detected.hpp>`
- __examples
- Suppose we wish to "reset" a value of type T, if the type has a `clear()` member function then we should call
- it, otherwise we should assign a default constructed value:
- template<class T>
- using clear_t = decltype(boost::declval<T&>().clear());
- template<class T>
- void clear(T& value)
- {
- if constexpr (boost::is_detected_v<clear_t, T>) {
- value.clear();
- } else {
- value = T();
- }
- }
- See also: __is_detected_convertible, __is_detected_exact.
- [endsect]
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