Constants and variables

Using constant has an impact on code readability. It makes code clearer and safer. Using constants instead of variables could also have performance benefits. When you use a constant you give the compiler a clear hint that this value won't be changed. The Swift compiler can apply inline optimization to use a value of that constant and not allocate memory for it.

In simple examples, the Swift compiler could do the same optimization for variables as well. Let's analyze the result for this simple example of iterating and calculating a sum. The performance is the same for variables and constants in this example.

var result = 0
for _ in 0...10000000 {
  let a = Int(arc4random())
  result += a
}
// Average Time - 0.162666518447804

var result = 0
for _ in 0...10000000 {
  var a = Int(arc4random())
  result += a
}
// Average Time - 0.160957522349781

If we look at a more complex example, we will see that constants perform the same as, or even better than, variables. It might...