tap

Header

#include <boost/hof/tap.hpp>

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.

Synopsis

template<class T, class F>
pipable constexpr T tap(T&& x, const F& f);

Requirements

F must be:

• 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);
}