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File indexing completed on 2025-01-18 09:38:17
0001 /*============================================================================= 0002 Copyright (c) 2014 Paul Fultz II 0003 tap.h 0004 Distributed under the Boost Software License, Version 1.0. (See accompanying 0005 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 0006 ==============================================================================*/ 0007 0008 #ifndef BOOST_HOF_GUARD_FUNCTION_TAP_H 0009 #define BOOST_HOF_GUARD_FUNCTION_TAP_H 0010 0011 /// tap 0012 /// === 0013 /// 0014 /// Description 0015 /// ----------- 0016 /// 0017 /// The `tap` function invokes a function on the first argument passed in and 0018 /// then returns the first argument. This is useful in a chain of pipable 0019 /// function to perform operations on intermediate results. As a result, this 0020 /// function is [`pipable`](/include/boost/hof/pipable). 0021 /// 0022 /// Synopsis 0023 /// -------- 0024 /// 0025 /// template<class T, class F> 0026 /// pipable constexpr T tap(T&& x, const F& f); 0027 /// 0028 /// Requirements 0029 /// ------------ 0030 /// 0031 /// F must be: 0032 /// 0033 /// * [UnaryInvocable](UnaryInvocable) 0034 /// 0035 /// Example 0036 /// ------- 0037 /// 0038 /// #include <boost/hof.hpp> 0039 /// #include <cassert> 0040 /// #include <iostream> 0041 /// using namespace boost::hof; 0042 /// 0043 /// struct sum_f 0044 /// { 0045 /// template<class T, class U> 0046 /// T operator()(T x, U y) const 0047 /// { 0048 /// return x+y; 0049 /// } 0050 /// }; 0051 /// 0052 /// const pipable_adaptor<sum_f> sum = {}; 0053 /// int main() { 0054 /// // Prints 3 0055 /// int r = 1 | sum(2) | tap([](int i) { std::cout << i; }) | sum(2); 0056 /// assert(r == 5); 0057 /// } 0058 /// 0059 0060 #include <boost/hof/pipable.hpp> 0061 #include <boost/hof/apply.hpp> 0062 #include <boost/hof/detail/static_const_var.hpp> 0063 0064 namespace boost { namespace hof { namespace detail { 0065 0066 struct tap_f 0067 { 0068 template<class T, class F> 0069 constexpr T operator()(T&& x, const F& f) const 0070 BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT((boost::hof::apply(f, x), BOOST_HOF_FORWARD(T)(x))) 0071 { 0072 return boost::hof::apply(f, x), BOOST_HOF_FORWARD(T)(x); 0073 } 0074 }; 0075 0076 } 0077 0078 BOOST_HOF_DECLARE_STATIC_VAR(tap, pipable_adaptor<detail::tap_f>); 0079 0080 0081 }} // namespace boost::hof 0082 0083 #endif
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