Golang Generics Exploration

main.go

package main

import (
	"fmt"
)

func main() {
	// One strategy is to include type info as the first 'n' parameters
	fmt.Println(genericAdd("int", 1, 2))
	fmt.Println(genericAdd("string", "1", "2"))
	
	// But if you want a typed return you need to specialize the functions
	intAdd := func(a, b int) int {
		return genericAdd("int", a, b).(int)
	}
	
	strAdd := func(a, b string) string {
		return genericAdd("string", a, b).(string)
	}
	
	fmt.Println(intAdd(1, 2))
	fmt.Println(strAdd("1", 2)) // type safety: don't compile!
	
	// The syntax with genericAdd2 looks cleaner, but has some faults:
	intAdd2 := genericAdd2("int")(1, 2)
	strAdd2 := genericAdd2("string")("1", 2) // you won't get this error at compile time = panic!
	
	fmt.Printf("%#v with type %T\n", intAdd2, intAdd2)
	fmt.Printf("%#v with type %T\n", strAdd2, strAdd2)
}

type Any interface{}

// Type T should be a real type instead of a string. Since we are returning a generic value
// we need an additional stage to make the type explicit again, hence the wrapper functions
// above.
func genericAdd(T string, a, b Any) Any {
	if T == "string" {
		return a.(string) + b.(string)
	}
	
	if T == "int" {
		return a.(int) + b.(int)
	}
	panic("unsuported type")
}

// Ideally we would be able to return a specialized function instead of a generic one
// in order to increase type safety at compile time. But the usage of this version is
// cleaner than the first one.
func genericAdd2(T string) func(a, b Any) Any {
	if T == "string" {
		// Current spec doesn't allow returning func(a, b string) string
		return func(a, b Any) Any {
			return a.(string) + b.(string)
		}
	}
	
	if T == "int" {
		// Current spec doesn't allow returning func(a, b int) int
		return func(a, b Any) Any {
			return a.(int) + b.(int)
		}
	}
	panic("unsuported type")
}

// How true generics would look like:

// func fakeGenericAdd(type T)(a, b T) T {
//	return a + b // panics if + is not implemented for type T
// }

// someInt := fakeGenericAdd(int)(1,2)
// someStr := fakeGenericAdd(string)("1",2)

https://play.golang.org/p/BjZX7KCx_L8