CODEWITHSUNDEEP
swiftoverriding
oxigen
oxigen

Reputation: 6263

Strange error "Declarations in extensions cannot override"

I can't understand, why in some cases I got error "Declarations in extensions cannot override" and in other cases - not.

Code:

protocol ConstrTest {
    var goodConstraints: [NSLayoutConstraint] {get}
    var badConstraints: [NSLayoutConstraint?] {get}
}

extension UIViewController: ConstrTest
{
    var goodConstraints: [NSLayoutConstraint] {
        return []
    }

    var badConstraints: [NSLayoutConstraint?] {
        return []
    }
}

class TestViewController: UIViewController {
    override var goodConstraints: [NSLayoutConstraint] {
        return []
    } //No errors and it works

    override var badConstraints: [NSLayoutConstraint?] {
        return []
    } //Got error Declarations in extensions cannot override
}

Why I can overide an array and can't override an optionals array?

Upvotes: 1

Views: 152

Answers (1)

Alain T.
Alain T.

Reputation: 42143

You cannot override a variable or function that you added to the base class using an extension. This may become possible in a future version of Swift.

The compiler may let you off with pure (or bridged) Objective-C types but as soon as you use a Swift type (e.g. an Optional or an Enum, etc.) you're going to get a compilation error.

Upvotes: 1

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