Optional Chaining as an alternative to forced unwrapping

？ And! The difference

You specify optional chaining by placing a question mark ( ? ) after the optional value on which we wish to call a prop Erty, method or subscript if the optional is non- nil . This was very similar to placing a exclamation mark () after a optional value to force the unwrapping of its ! value. The main difference is this optional chaining fails gracefully when nil the optional is, whereas forced unwrapping Trigg ERs a runtime error when the optional is nil .

Query value is optional type

To reflect the fact that optional chaining can being called on a nil value, the result of an optional chaining Always an optional value,

Specifically, the result of a optional chaining call is of the the same type as the expected return value Optional.

1. let roomCount = john.residence!.numberOfRooms
2. // this triggers a runtime error

accessing subscripts Through Optional Chaining

You can use optional chaining to try to retrieve and set a value from a subscript on an optional value, and to check Wheth Er that subscript call is successful.

accessing subscripts of Optional Type

If a subscript Returns a value of optional Type-such as the key subscript of Swift ' s Dictionary type-place a question mark after the subscript's closing bracket to chain in its optional return value:

1. var testscores = [ "Dave": [86, 82, 84], "Bev": [ 94, 81]]
2. testscores[ "Dave"]?[ 0] = 91
3. < Span class= "VC" >testscores[ "Bev"]?[ 0] + = 1
4. < Span class= "VC" >testscores[ "Brian"]?[ 0] = 72
5. < span class= "C" >//the "Dave" Array is now [,, +] and the "Bev" array is now [+, 94, Bayi]

Optional Chaining as an alternative to forced unwrapping