thing_tells_how_to_apply.go

// I am applying function on two things and they tell me how 🐁
// https://go.dev/play/p/8iGGh8Tebgw
package main

import "fmt"

type Summer interface {
	Sum(other Summer) Summer
}

type AddSummer struct {
	X int
	Y int
}

func (s AddSummer) Sum(other Summer) Summer {
	v, ok := other.(AddSummer)
	if !ok {
		return s
	}

	return AddSummer{
		X: s.X + v.X,
		Y: s.Y + v.Y,
	}
}

func sum(s []Summer) Summer {
	t := s[0]
	for i, q := range s {
		if i == 0 {
			continue
		}
		t = t.Sum(q)
	}
	return t
}

func main() {
	s := AddSummer{X: 1, Y: 1}

	v := sum([]Summer{s, s, s, s})

	fmt.Printf("%#v", v)
}