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add downcast to the tutorial

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hamidra 2019-11-01 20:49:53 -07:00 committed by GitHub
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commit 9c18774c34
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@ -692,6 +692,11 @@ print(mySquare.sideLength) // 4
// cast instance
let aShape = mySquare as Shape
// downcast instance:
// Because downcasting can fail, the result can be an optional (as?) or an implicitly unwrpped optional (as!).
let anOptionalSquare = aShape as? Square // This will return nil if aShape is not a Square
let aSquare = aShape as! Square // This will throw a runtime error if aShape is not a Square
// compare instances, not the same as == which compares objects (equal to)
if mySquare === mySquare {
print("Yep, it's mySquare")