Returning From Functions in Go

We can pass values into a function with arguments. We can also use a return statement to send a value back out of a function.

In Go, a function that returns a value declares the return type after the parameter list:

func plusThree(num int) int {
    return num + 3
}

When execution reaches return, the function stops and sends the value back to the calling code:

func plusThree(num int) int {
    return num + 3
}

func mainFunction() {
    answer := plusThree(5)
    fmt.Println(answer) // Output: 8
}

Using a returned value

The returned value can be stored in a variable, printed, or used in another expression.

func getMessage(name string, language string) string {
    return "Hey, " + name + "! Welcome to " + language + "!"
}

func mainFunction() {
    message := getMessage("Andy", "Java")
    fmt.Println(message)
}

No return statement

In Go, if a function declares a return type, it must return a value of that type. A function declared with string must return a string, and a function declared with int must return an integer.

Multiple returns & error handling:

Unlike most languages, a Go function can return several values at once. The common idiom is to return a result and an error, then check the error before using the result.

func half(n int) (int, error) {
    if n%2 != 0 {
        return 0, fmt.Errorf("odd number")
    }
    return n / 2, nil
}

v, err := half(10)
if err != nil {
    // handle the error
}
fmt.Println(v) // 5

That v, err := f() followed by if err != nil pattern appears all over the coding tutorials — it's how Go reports failures instead of throwing exceptions.

Assignment
Follow the Coding Tutorial and let's write a function that returns a value.

Hint
Look at the examples above if you get stuck.