CODEWITHSUNDEEP
swiftxcodegenerics
Sergey Hleb
Sergey Hleb

Reputation: 92

Overriding a generic function produce an error

I am writing a generic function in a protocol, but an error occurs when overriding this function in inherited classes.

The first way i use

protocol BaseCellProtocol {
    associatedtype T
    func configure<T>(with object: T?)  
}

class TableViewCell: BaseTableViewCell {

    typealias T = String

    override func configure<T>(with object: T?) {
        label.text = object as? T
    }

}

But this way produce an error:

Cannot assign value of type 'T?' to type 'String?'

T was overrided in class as String, but compiler don't understand that T is String

The second way

protocol BaseCellProtocol {
    func configure<T>(with object: T?)
}

class TableViewCell: BaseTableViewCell {

    override func configure<String>(with object: String?) {
        label.text = object
    }

}

In this case, the error is:

Cannot assign value of type 'String?' to type 'String?'

Whaaaaat?

I am new to generics, I read some literature, but I have some problems with this.

update 

class BaseTableViewCell: UITableViewCell, BaseCellProtocol {

    typealias T = String

    func configure<T>(with object: T?) {
    }

}

Upvotes: 4

Views: 68

Answers (1)

Thanh Vu
Thanh Vu

Reputation: 1739

Just remove <T> in function. Because you have T in typealias.

protocol BaseCellProtocol {
    associatedtype T
    func configure(with object: T?)
}

class BaseTableViewCell: UITableViewCell, BaseCellProtocol {

    typealias T = String

    func configure(with object: T?) {
    }
}

class TableViewCell: BaseTableViewCell {

    override func configure(with object: String?) {
        label.text = object
    }
}

Upvotes: 2

Related Questions