Match optional in switch statement

Question

Given a non-optional value, how can I match against an optional in a switch statement?

For example:

let test = "some string"

let x: String? = nil
let y: String? = "some string"
let z: String? = "another string"

switch test {
case x:
    print(x)
case y:
    print(y)
case z:
    print(z)
default: break
}

results in:

Expression pattern of type 'String?' cannot match values of type 'String'

for each case...

I've read the swift docs on patterns and switch but I can't seem to find a way of making this work.

I know I can work around this, but there must be a way of making this work...

Edit

As requested, here is my actual use case. Note all text fields are optional...

    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        // TODO: Replace with switch if possible

//        switch textField {
//        case nameTextField:
//            usernameTextField?.becomeFirstResponder()
//        case usernameTextField:
//            dateOfBirthTextField?.becomeFirstResponder()
//        case dateOfBirthTextField:
//            phoneTextField?.becomeFirstResponder()
//        case phoneTextField:
//            phoneTextField?.resignFirstResponder()
//        default: break
//        }

        if textField == nameTextField {
            usernameTextField?.becomeFirstResponder()
        } else if textField == usernameTextField {
            dateOfBirthTextField?.becomeFirstResponder()
        } else if textField == dateOfBirthTextField {
            phoneTextField?.becomeFirstResponder()
        } else if textField == phoneTextField {
            phoneTextField?.resignFirstResponder()
        }
        return false
    }

For me this is actually too general a question. You have to be facing something more specific - something less "theoretical". Could you post that code? — user7014451
– user7014451, Commented Oct 28, 2017 at 4:09

Jaydeep Vora · Accepted Answer · 2017-10-28 04:14:42Z

2

Swift 4.0

You can check with optional case as like below. Hope this will help you.

let test = "some string"

let x: String? = nil
let y: String? = "some string"
let z: String? = "another string"

switch test {
case let val where val == x:
    print(x)
case let val where val == y:
    print(y)
case let val where val == z:
    print(z)
default:
    break
}

answered Oct 28, 2017 at 4:14

Jaydeep Vora

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Comments

Martin R · Accepted Answer · 2017-10-28 14:44:15Z

For your actual use-case: I would create an array of all non-nil text fields. Then you can lookup the current text field in that array and make the next one in the list the first responder:

let fields = [nameTextField, usernameTextField, dateOfBirthTextField, phoneTextField]
    .flatMap { $0 }
if let idx = fields.index(of: textField), idx + 1 < fields.count {
    fields[idx + 1].becomeFirstResponder()
} else {
    textField.resignFirstResponder()
}

This is less error-prone and can easily be modified if the number or order of the text fields changes.

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