Functions

Functions

Define functions with func.

// If both are same type
func name(param1, param2 string) {}

// If different types
func name(param1 int, param2 string) {}

Return types

func name(param1, param2 string) string {
    return param1
}

Return multiple values

func name(param1 int, param2 string) (int, string) {
    return param1, param2
}

var a, b string = name("A", "B")

Auto declare & return variables

Specify names of returned variables, and Go will auto declare AND return them, when return is called.

// No auto declaring & return
func name(param1 int, param2 string) (int, string) {
    var ra = param1
    var rb = param2
    return ra, rb
}

// Auto declare & return
func name(param1 int, param2 string) (ra int, rb string) {
    ra = param1
    rb = param2
    return
    // Or you can explicitly return them though
    return ra, rb
}

Functions as parameters

func upper(text string) string {}

func name(param1 string, transform func(string) string)  {
    return transform(param2)
}

a := name("a", upper)

Functions as values

func upper(text string) string {}
func lower(text string) string {}

func decide(whichOne string) func(string) string {
    if ... {
        return upper
    }
    return lower
}

f := decide("upper") // f will have the upper function
f("a") // A

Anonymous functions

func name(param1 string, transform func(string) string)  {
    return transform(param2)
}

a := name("a", func (text string) string {
    ...
})

Variadic functions

Functions that work with any amount of parameters.

func name(numbers ...int) int[] {
    return numbers
}

Add other parameters, but only BEFORE the numbers parameter.

func name(name string, numbers ...int) int[] {
    return numbers
}

Closures

A closure is a function that captures variables from an outer scope.

Closures can lead to unexpected behavior in Concurrency.

In the example bellow, count is remembered through increment executions, because counter ends up allocated in the heap since the anonymous function references it.

Referencing a outer scope variable is always by reference, that is how the value is changed.

And because of the allocation in the Heap, it will not be Garbage Collected until the reference is lost.

func counter() func() int  {
    counter := 0
    return func () int {
        count++
        return count
    }
}

increment := counter()
increment() // 1
increment() // 2
increment() // 3

The main() function

There is also the need for a main() function to be defined. Which will be the entrypoint function by default to be executed.

There can only be ONE main() function in your package main.

If making a utility package there is no need for a main() function. Because it is not intended to be executed as a program, but to be imported by other packages.