Passing arguments to functions in Golang

Functions wouldn't be much use if we couldn't pass parameters to them. Rewriting our previous example, we might decide to create a function that takes a string as it's single argument.

package main

import "fmt"

func saySomething(somethingToSay string) {
    fmt.Println(somethingToSay)
}

func main() {
    saySomething("Hello")
    saySomething("world")
}

We've declared a function saySomething that takes a single argument. The argument is a string type and is called somethingToSay. We then use our new function, calling it twice from our main func to output:

Hello
wordl

Go also provides first class functions. This means we can pass a function as an argument into another function. For example:

package main

import "fmt"

func hello(aFunc func(words string) string) {
    fmt.Println(aFunc("Hello"))
}


func main() {

    var x = func(words string) string {
        return words + " world"
    }
    hello(x)

}

Again, all our program does is print

Hello world

, though in a roundabout way. We've defined a function hello which accepts as its argument another function - note that the argument defines the signature of the function we expect to receive - in this case, a function that takes one string argument and returns a string. Moving into our main function, we define x to be a function that will append " world" onto whatever string is passed in. This is rather convoluted, but illustrates the point. Now, if we fancy, we can define a goodbye function as well - to wit:

package main

import "fmt"

func goodbye(aFunc func(words string) string) {
    fmt.Println(aFunc("Goodbye"))
}

func hello(aFunc func(words string) string) {
    fmt.Println(aFunc("Hello"))
}


func main() {

    var x = func(words string) string {
        return words + " world"
    }
    hello(x)
    goodbye(x)

}

Now our program outputs the following:

Hello world
Goodbye world

Now our code is ripe for a refactor - we have duplicate argument definitions, which we can code out - but we will leave that to another post.