Functions – the basics

Here is how you write a function in Go:

func main(){
//do something
}

The main function is almost always the first function that gets executed in your Go program. The main function needs to live inside the main package, since main is the entry point package for your Go program.

Here is what a function with arguments would look like:

func add(a int, b int){
//a+b
}

Since the a and b arguments from the preceding code are of the same type, we can also do this:

func add(a,b int){
//a+b
}

Now, let's say we want to return a value from our function. Here is what this would look like:

func add(a,b int)int{
return a+b
}

Go also allows multiple returns, so you can do this:

func addSubtract(a,b int)(int,int){
return a+b,a-b
}

In Go, there is a concept known as named returns, which basically means that you can name your return values in the function header. Here is what this looks like:

func addSubtract(a,b int)(add,sub int){
add = a+b
sub = a-b
return
}

Functions are also first-class citizens in the Go language, which means that you can assign a function to a variable and use it as a value. Here is an example:

var adder = func(a,b int)int{
return a+b
}
var subtractor = func(a,b int) int{
return a-b
}
var addResult = adder(3,2)
var subResult = subtractor(3,2)

Because of this, you can also pass functions as arguments to other functions:

func execute(op func(int,int)int, a,b int) int{
return op(a,b)
}

Here is an example of us making use of the execute function we defined previously:

var adder = func(a, b int) int {
    return a + b
}
execute(adder,3,2)

Go also supports the concept of variadic functions. A variadic function is a function that can take an unspecified number of arguments. Here is an example of an adder function that takes an unspecified number of int arguments and then adds them:

func infiniteAdder(inputs ...int) (sum int) {
  for _, v := range inputs {
    sum += v
  }
  return
}

The preceding function takes any number of int arguments and then sums them all. We'll cover the for..range syntax here later in this chapter, under the Conditional statements and loops section. We can then call our new function using the following syntax:

infiniteAdder(1,2,2,2) // 1 + 2 + 2 + 2

We'll look at how functions can be accessed from other packages in the next section.