money_pure.go

// https://go.dev/play/p/mcWx20GtkaO
// 🌊
package main

import "fmt"

type SGD int64

func (as SGD) Add(bs SGD) SGD { return as + bs }

type KRW int64

func (ak KRW) Add(bk KRW) KRW { return ak + bk }

type Money interface {
	SGD | KRW
}

func logic[T Money](a T, b T) T {
	return a + b
}

func nestedLogic[T Money](a T, b T) T {
	return logic[T](a, b)
}

func main() {
	//compile error
	//x := (SGD)(10) + (KRW)(1000)
	//fmt.Println(x)

	y := (SGD)(10) + (SGD)(11)
	fmt.Println(y)

	z := logic[SGD](10, 11)
	fmt.Println(z)

	// not compiles
	//fmt.Println(logic[SGD](10, (KRW)(1)))
	//fmt.Println(nestedLogic[SGD](10, (KRW)(1)))
}

since not struct, big issue with mixing with untyped constants