Golang func - return type

This is my first Golang program after 'Hello world'. Please find following code block which aims to perform basic arithmetic and multiple type return demo. This is just a hypothetical sample to learn Go func. However, I am getting following exception on compilation. From exception, i assume, operations on int8 operand return int16/int32 as return type and which is not correct as per go.

Question: Isn't it safe for language to assume int8 is safely assignable to int16 or int32

package main
import (
	"fmt"
)
func Arithmetic(a,b int8) (int8,string,int16,int32){
	return a-b, "add",a*b,a/b
}
func main() {
	a,b,c,d :=Arithmetic(5,10)
	fmt.Println(a,b,c,d)
}

Error:

C:/Go\bin\go.exe run C:/GoWorkspace/src/tlesource/ff.go
# command-line-arguments
.\ff.go:15: cannot use a * b (type int8) as type int16 in return argument
.\ff.go:15: cannot use a / b (type int8) as type int32 in return argument

Process finished with exit code 2

> Is it it safe for language to assume int8 is safely assignable to int16 or int32

Yes, It would be, if Go did implicit conversions on assignment. But it does not (only interface-wrapping when applicable).

There are several reasons:

• The concept of automatic conversion cannot be generalized to all types without introducing the concept of a type hierarchy. And, as you know, all concrete types in Go are invariant.
• Go is "anti-magic" and in this spirit it doesn't do stuff you did not request it to do (except e.g. write-barriers on pointers).

The error says that you have to return int16 and int32, all you have to do is convert the result like this:

func Arithmetic(a, b int8) (int8, string, int16, int32) {
	return a - b, "add", int16(a * b), int32(a / b)
}