1. Function as a reference type
2. Function as a variable

Try to create as many let variable as possible to conserve memory.

1. Function as a reference type

Arguments of functions are a let constant . Below code will give error.

func add(a: Int, b: Int) {
		a = 10
    let sum = a + b
    print(sum)
}

add(a: 10, b: 5)

To update the value of instance scope by a function using inout

using this function we update the value of variable.

var number = 5 // instance scope

// inside of a funciton local scope
// funciton pass by reference
func addNumber(a: inout Int) {
    a += 10
}

addNumber(a: &number)
print(number)

Swapping two numbers using inout in a function

var x = 5
var y = 10

func swap(x: inout Int, y: inout Int) {
    let temp = x
    x = y
    y = temp
}

swap(x: &x, y: &y)
print("x = \(x) and y = \(y)")

Output:

x = 10 and y = 5

2. Function as a variable