Empty Go Interfaces

When declaring function parameters in Go, you must type the incoming data. Here’s an example:

package main

import "fmt"

func print_stuff(s string) {
    fmt.Println(s)
}

func main() {
    print_stuff("Passing string!")
}

s string indicates that we’re passing a variable of type string into the function. This prevents us from from passing into variables of any other type. For example, this will fail with ./prog.go:10:17: cannot use 42 (type untyped int) as type string in argument to example_str if you try to pass an integer.

package main

import "fmt"

func print_stuff(s string) {
    fmt.Println(s)
}

func main() {
    print_stuff(42)  // Fails!
}

Empty Go interfaces can be used to accept any type of variable in a function.

package main

import "fmt"

func print_stuff(s interface{}) {
    fmt.Println(s)
}

func main() {
    print_stuff(42) // Now works fine!
}

Typically you should properly type your variables, but in some cases (where you cannot know the type of data ahead of time), this can be useful.

fmt.Println() is a good example of this.