Swift Tutorial - Tutorialspoint

The process of querying, calling properties, subscripts and methods on an optional that
may be 'nil' is defined as optional chaining. Optional chaining return two values:

 if the optional contains a 'value' then calling its related property, methods and

subscripts returns values

 if the optional contains a 'nil' value all its its related property, methods and

subscripts returns nil

Since multiple queries to methods, properties and subscripts are grouped together failure
to one chain will affect the entire chain and results in 'nil' value.

Optional Chaining as an Alternative to Forced Unwrapping

Optional chaining is specified after the optional value with '?' to call a property, method or
subscript when the optional value returns some values.

Optional Chaining '?'

Access to methods,properties and

subscriptsOptional Chaining '!' to force

Unwrapping

? is placed after the optional value to

call property, method or subscript

! is placed after the optional value to call

property, method or subscript to force

unwrapping of value

Fails gracefully when the optional is 'nil'

Forced unwrapping triggers a run time error

when the optional is 'nil'

Program for Optional Chaining with '!'

class ElectionPoll {

var candidate: Pollbooth?

}

class Pollbooth {

var name = "MP"

}

let cand = ElectionPoll()

let candname = cand.candidate!.name

28. SWIFT – OPTIONAL CHAINING........................................................................................