Swift: testing against optional value in switch case - swift

Question

In Swift, how can I write a case in a switch statement that tests the value being switched against the contents of an optional, skipping over the case if the optional contains nil?
Here's how I imagine this might look:
let someValue = 5
let someOptional: Int? = nil
switch someValue {
case someOptional:
// someOptional is non-nil, and someValue equals the unwrapped contents of someOptional
default:
// either, someOptional is nil, or someOptional is non-nil but someValue does not equal the unwrapped contents of someOptional
}
If I just write it exactly like this, the compiler complains that someOptional is not unwrapped, but if I explicitly unwrap it by adding ! to the end, I of course get a runtime error any time someOptional contains nil. Adding ? instead of ! would make some sense to me (in the spirit of optional chaining, I suppose), but doesn't make the compiler error go away (i.e. doesn't actually unwrap the optional).

Answer 1

Optional is just a enum like this:
enum Optional<T> : Reflectable, NilLiteralConvertible {
case none
case some(T)
// ...
}
So you can match them as usual "Associated Values" matching patterns:
let someValue = 5
let someOptional: Int? = nil
switch someOptional {
case .some(someValue):
println("the value is \(someValue)")
case .some(let val):
println("the value is \(val)")
default:
println("nil")
}
If you want match from someValue, using guard expression:
switch someValue {
case let val where val == someOptional:
println(someValue)
default:
break
}
And for Swift > 2.0
switch someValue {
case let val where val == someOptional:
print("matched")
default:
print("didn't match; default")
}

Answer 2

As of Xcode 7, “a new x? pattern can be used to pattern match against optionals as a synonym for .some(x)”. This means that in Swift 2 and later the following variation of rintaro's answer will work as well:
let knownValue = 5
switch someOptional {
case knownValue?:
// Contents of someOptional are knownValue, defined above.
case let otherValue?:
// Contents of someOptional are *any* non-nil value not already tested for.
// Unwrapped contents are assigned to otherValue for use inside this case.
default:
// someOptional is nil.
}

Answer 3

In Swift 4 you can use Optional of Apple to wrappe optional
https://developer.apple.com/documentation/swift/optional
Example
enum MyEnum {
case normal
case cool
}
some
let myOptional: MyEnum? = MyEnum.normal
switch smyOptional {
case .some(.normal):
// Found .normal enum
break
case .none:
break
default:
break
}
none
let myOptional: MyEnum? = nil
switch smyOptional {
case .some(.normal):
break
case .none:
// Found nil
break
default:
break
}
default
let myOptional: MyEnum? = MyEnum.cool
switch smyOptional {
case .some(.normal):
break
case .none:
break
default:
// Found .Cool enum
break
}
Enum with value
enum MyEnum {
case normal(myValue: String)
case cool
}
some value
let myOptional: MyEnum? = MyEnum.normal("BlaBla")
switch smyOptional {
case .some(.normal(let myValue)) where myValue == "BlaBla":
// Here because where find in my myValue "BlaBla"
break
// Example for get value
case .some(.normal(let myValue)):
break
// Example for just know if is normal case enum
case .some(.normal):
break
case .none:
break
default:
break
}

Answer 4

You can explicitly mention all cases along with nil as an additional case to handle the optional:
switch optionalEnumValue {
case .caseOne:
break
case .caseTwo:
break
case .caseN:
break
case nil:
break
}