guard let shadow.swift

var x : Int? = 10
//arguments
func foo(arg : Int?) {
    guard let arg = arg else {
        return
    }
    print(arg)
}
foo(arg:x)

//global variable
guard let x = x else { throw NSError() }
print(x)

//local variable
func bar() {
    let y : Int? = 100
    guard let y = y else { return }
    print(y)
}