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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.


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let x = 10
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fun f(): Int {
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let y = 10
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return x + y
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}
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f() // is `20`
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// Invalid: the identifier `y` is not in scope.
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//
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y


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fun doubleAndAddOne(_ n: Int): Int {
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fun double(_ x: Int) {
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return x * 2
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}
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return double(n) + 1
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}
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// Invalid: the identifier `double` is not in scope.
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//
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double(1)

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


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let x = 2
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fun test(): Int {
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let x = 3
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return x
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}
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test() // is `3`

Scope is lexical, not dynamic.


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let x = 10
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fun f(): Int {
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return x
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}
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fun g(): Int {
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let x = 20
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return f()
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}
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g() // is `10`, not `20`

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


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let x = 2
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fun f(): Int {
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if x == 0 {
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let x = 3
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return x
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}
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return x
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}
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f() // is `2`