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 >).


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


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


F must be:

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));


#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);