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-rw-r--r--swift.html.markdown5
1 files changed, 5 insertions, 0 deletions
diff --git a/swift.html.markdown b/swift.html.markdown
index 1f9fe897..8582131a 100644
--- a/swift.html.markdown
+++ b/swift.html.markdown
@@ -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")