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