Cannot assign to self in a method - Swift

Question

In Xcode 6.1 and with the blog post about Failable Initializers on the Swift Blog, Apple has assigned to self in a failable initializer.

The Int (init(fromString:)) example on the blog post compiles fine when copied into my project with an assignment to self, but trying this with a custom class in my own code results in the usual error "Cannot assign to 'self' in a method".

extension Contact {
    public convenience init?(context: NSManagedObjectContext = DataStore.managedObjectContext) {
        if let userId = User.loggedInUserId(context) {
            let contact = NSEntityDescription.insertNewObjectForEntityForName("Contact", inManagedObjectContext: context) as Contact

            self = contact
        } else {
            return nil
        }
    }
}

(Contact is a subclass of NSManagedObject)

Is there anything I am missing with failable initializers?

Awesome answer : http://stackoverflow.com/a/27647411/3411787 — Mohammad Zaid Pathan, Sep 28 '16 at 19:13

rintaro · Accepted Answer · 2014-10-21T01:18:29.673

Assigning to self is for value types only, struct and enum.

In your case you should do like this:

public convenience init?(context: NSManagedObjectContext) {
    let entity = NSEntityDescription.entityForName("Contact", inManagedObjectContext: context);
    self.init(entity: entity!, insertIntoManagedObjectContext: context)

    if  User.loggedInUserId(context)  == nil {
        context.deleteObject(self)
        return nil
    }
}

You must call self.init(..) unconditionally, because, it's a rule for convenience initializer. If the condition is false, deleteObject(self) and return nil. Hmm... I think you should not use failable initializers for this.

Wouldn't have to delete except it seems you have to call self.init(entity before returning nil. Can't do the checks before calling the designated initialiser. — Damien Pontifex, Oct 21 '14 at 01:44

score 0 · Answer 2 · answered Oct 21 '14 at 00:36

0

A convenience initializer must call a designated initializer from the same class. Instead of assigning to self, can you create a designated initializer that takes and copies a Contact instance?

answered Oct 21 '14 at 00:36

Nate Cook

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Cannot assign to self in a method - Swift

2 Answers2