infix — Boost.HigherOrderFunctions 0.6 documentation

# infix

## Header

    #include <boost/hof/infix.hpp>

## Description

The `infix` function adaptor allows the function to be used as an infix operator. The operator must be placed inside the angle brackets(ie `<` and `>`).

## Synopsis

    template<class F>
    constexpr infix_adaptor<F> infix(F f);

## Semantics

    assert(x <infix(f)> y == f(x, y));

## Requirements

F must be:

- BinaryInvocable
- MoveConstructible

## Operator precedence

Infix operators have the precedence of relational operators. This means operators such as `+` or `*` have higher precedence:

    assert((x + y <infix(f)> z) == ((x + y) <infix(f)> z));
    assert((x * y <infix(f)> z) == ((x * y) <infix(f)> z));

However, operators such as `|` or `==` have lower precedence::

    assert((x | y <infix(f)> z) == (x | (y <infix(f)> z)));
    assert((x == y <infix(f)> z) == (x == (y <infix(f)> z)));

Also, infix operators have left-to-right associativity:

    assert(x <infix(f)> y <infix(g)> z == ((x <infix(f)> y) <infix(g)> z));

## Example

    #include <boost/hof.hpp>
    #include <cassert>
    using namespace boost::hof;

    struct plus_f
    {
        template<class T, class U>
        T operator()(T x, U y) const
        {
            return x+y;
        }
    };

    int main() {
        constexpr infix_adaptor<plus_f> plus = {};
        int r = 3 <plus> 2;
        assert(r == 5);
    }