Go’s compiler is smart enough to spot division by zero errors

I’ve been doing a couple of Go experiments, and I wanted to test if Go has lazy evaluation of if conditions.

I wrote the following simple program – the first condition is true, so I’m looking for Go to print the message on line 7 rather than try to evaluate the invalid condition:

package main

import "fmt"

func main() {
	if 2%2 == 0 || 1/0 == 0 {
		fmt.Println("one of these conditions is true")
	}
}

But surprisingly, Go won’t let me compile this program:

$ go run division.go
# command-line-arguments
./division.go:6:19: invalid operation: division by zero

This also works if your divisor is a const – presumably the compiler inlines it at some point, and notices the same mistake. This code fails for a similar reason:

const divisor = 0

if 2%2 == 0 || 1/divisor == 0 {
	fmt.Println("one of these conditions is true")
}

But it’s fine if your divisor is a regular variable. This makes sense – the compiler can’t know if the value might change at runtime and make this a legal operation. This code compiles and runs successfully, which also proves that Go is doing lazy evaluation of if conditions:

divisor := 0

if 2%2 == 0 || 1/divisor == 0 {
	fmt.Println("one of these conditions is true")
}

Finally, if you change the program so it does evaluate that branch:

divisor := 0

if 1%2 == 0 || 1/divisor == 0 {
	fmt.Println("one of these conditions is true")
}

then you get a runtime error:

$ go run division.go
panic: runtime error: integer divide by zero

goroutine 1 [running]:
main.main()
	/var/folders/lp/1yl_g9ls2_g3l2tkmb6fpg0h0000gn/T/tmp.bQHLQIAYxc/division.go:8 +0x1c
exit status 2