Scope

Every function and block ({ ... }) introduces a new scope for declarations. Each function and block can refer to declarations in its scope or any of the outer scopes.

_12

let x = 10

_12

_12

fun f(): Int {

_12

let y = 10

_12

return x + y

_12

}

_12

_12

f() // is `20`

_12

_12

// Invalid: the identifier `y` is not in scope.

_12

//

_12

y

_10

fun doubleAndAddOne(_ n: Int): Int {

_10

fun double(_ x: Int) {

_10

return x * 2

_10

}

_10

return double(n) + 1

_10

}

_10

_10

// Invalid: the identifier `double` is not in scope.

_10

//

_10

double(1)

Each scope can introduce new declarations, i.e., the outer declaration is shadowed.

_10

let x = 2

_10

_10

fun test(): Int {

_10

let x = 3

_10

return x

_10

}

_10

_10

test() // is `3`

Scope is lexical, not dynamic.

_12

let x = 10

_12

_12

fun f(): Int {

_12

return x

_12

}

_12

_12

fun g(): Int {

_12

let x = 20

_12

return f()

_12

}

_12

_12

g() // is `10`, not `20`

Declarations are not moved to the top of the enclosing function (hoisted).

_10

let x = 2

_10

_10

fun f(): Int {

_10

if x == 0 {

_10

let x = 3

_10

return x

_10

}

_10

return x

_10

}

_10

f() // is `2`