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swiftoption-type

Most elegant way to compare two optionals in Swift

I have two AnyObject? variables that I would like to compare for reference equality:

var oldValue: AnyObject?
var newValue: AnyObject?
...
if oldValue != newValue {
    changed = true
}

This doesn't work though, as I apparently cannot compare two optionals directly. I want the behavior as if I were comparing ids in Objective-C, that is:

  • true if both are nil
  • true if both have a value and the values are also equal
  • false otherwise

Is there an elegant way to write this in Swift (ideally without having to write a custom extension)?

This is the best I've come up with:

if !(oldValue != nil && newValue != nil && oldValue == newValue)

Not very pretty. :(

Solution

  • You can use !==

    From The Swift Programming Language

    Swift also provides two identity operators (=== and !==), which you use to test wether two objects references both refer to the same object instance.

    Some good examples and explanations are also at Difference between == and ===

    On @PEEJWEEJ point, doing the following will result in false

    var newValue: AnyObject? = "String"
var oldValue: AnyObject? = "String"

if newValue === oldValue {
   print("true")
} else {
   print("false")
}