03.Functions.slide

# Functions

## function saga
    We've already seen functions being declared and used. Every program we've 
    written has a main function that's the starting point for every Go program

    A function declaration has four parts: the keyword func, the name of the function, 
    the input parameters, and the return type.

    Syntax:
        func <fun_name>(args...) <return_type> {
            return <type>
        }
    
    Just like other languages, Go has a return keyword for returning values from a function

.code -numbers -edit code/functions/add.go /^func add/,/^}/

.play -numbers -edit code/functions/add.go /^func main/,/^}/

## variadic input 

.code -numbers -edit code/functions/variadic_input.go /^func addTo/,/^}/

.play -numbers -edit code/functions/variadic_input.go /^func main/,/^}/

## Multiple Return Values

.code -numbers -edit code/functions/return_values.go /^func divAndRemainder/,/^}/

.play -numbers -edit code/functions/return_values.go /^func main/,/^}/


## Functions Are Values
    The type of a function is built out of the keyword func and the types of the parameters 
    and return values. This combination is called the signature of the function. Any function 
    that has the exact same number and types of parameters and return values meets the type signature.

.code -numbers -edit code/functions/functions_as_values.go /^func add/,/^}/

.play -numbers -edit code/functions/functions_as_values.go /^func main/,/^}/

## Anonymous Functions

.play -numbers -edit code/functions/anonymous_func.go /^func main/,/^}/

## defer

    Programs often create temporary resources, like files or network connections, 
    that need to be cleaned up. This cleanup has to happen, no matter how many exit
    points a function has, or whether a function completed successfully or not. 
    In Go, the cleanup code is attached to the function with the defer keyword.

.play -numbers -edit code/functions/defer.go /^func main/,/^}/

## 
<h2>GO is call by value !</h2>