Redeclaration of a Constant inside a function

variables and constants declared inside a function are "local" and scoped to that function. they come into existence when the function is called and cease to exist once it finishes executing. nothing outside of the function even knows about things that happen inside the function.

the function does not care or know about anything it did in previous times it was called. each time its called its a new day for everything that happens inside it.

the area constant is not being redeclared each time, its just being declared since really its like the area constant never existed before.

On the other hand, if you declare a constant outside a function it has a global scope so something like this would generate a redeclaration error:

// not inside a function, so it has global scope, not local
let area = 15
//error: redeclaration of a constant 
let area = 16

because variables and constants declared inside a function are local and scoped to that function, you could declare a constant outside a function, and then declare another with the same name and it would be valid, since the constant inside the function is local to that function, and thus a completely different entity:

let area = 15

func doSomething() {

// perfectly fine
// this area constant is different than the area constant above. this is a local constant
let area = 16
}