go functions receiving nils

Wed, 10 Dec 2025 00:00:00 +0000

About

A few gotchas when using nil as function arguments in golang.

Studies

The zero value of a slice is nil:

  var s []string
  if s == nil {
  	fmt.Println("s is nil!") // XXX: we will see this printed.
  }

However, when s is passed to a function that accepts an interface, then it is no longer true!

  func run(something any) {
  	if something == nil {
  		fmt.Println("something is nil!")
  	} else {
  		fmt.Println("something is not nil!")
  	}
  }

  func main() {
  	var s []string
  	run(s) // XXX: s is not nil!

This is because in any is an interface, and a comparison operation on an interface compares two things: the interface's type, and the interface's value.

Go on August Feng

go functions receiving nils

About

Studies