/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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tap.h
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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==============================================================================*/
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#ifndef BOOST_HOF_GUARD_FUNCTION_TAP_H
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#define BOOST_HOF_GUARD_FUNCTION_TAP_H
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/// tap
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/// ===
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///
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/// Description
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/// -----------
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///
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/// The `tap` function invokes a function on the first argument passed in and
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/// then returns the first argument. This is useful in a chain of pipable
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/// function to perform operations on intermediate results. As a result, this
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/// function is [`pipable`](/include/boost/hof/pipable).
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///
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/// Synopsis
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/// --------
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///
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/// template<class T, class F>
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/// pipable constexpr T tap(T&& x, const F& f);
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///
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/// Requirements
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/// ------------
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///
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/// F must be:
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///
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/// * [UnaryInvocable](UnaryInvocable)
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///
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/// Example
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/// -------
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///
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/// #include <boost/hof.hpp>
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/// #include <cassert>
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/// #include <iostream>
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/// using namespace boost::hof;
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///
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/// struct sum_f
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/// {
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/// template<class T, class U>
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/// T operator()(T x, U y) const
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/// {
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/// return x+y;
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/// }
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/// };
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///
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/// const pipable_adaptor<sum_f> sum = {};
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/// int main() {
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/// // Prints 3
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/// int r = 1 | sum(2) | tap([](int i) { std::cout << i; }) | sum(2);
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/// assert(r == 5);
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/// }
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///
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#include <boost/hof/pipable.hpp>
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#include <boost/hof/apply.hpp>
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#include <boost/hof/detail/static_const_var.hpp>
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namespace boost { namespace hof { namespace detail {
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struct tap_f
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{
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template<class T, class F>
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constexpr T operator()(T&& x, const F& f) const
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BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT((boost::hof::apply(f, x), BOOST_HOF_FORWARD(T)(x)))
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{
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return boost::hof::apply(f, x), BOOST_HOF_FORWARD(T)(x);
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}
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};
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}
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BOOST_HOF_DECLARE_STATIC_VAR(tap, pipable_adaptor<detail::tap_f>);
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}} // namespace boost::hof
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#endif
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