In Swift, how to create convenience initialization for a class, where the init implementation creates a class value instead of calling an existing init

Question

It seems to me that the answer is obvious, but I could not understand it, and for me this is a recurring problem. Basically I want to do something like this:

extension NSData {
    convenience init(JSONObject: AnyObject) {
        do {
            self = try NSJSONSerialization.dataWithJSONObject(JSONObject, options: [])
        }
        catch {
            self = nil
        }
    }
}

However, he will not allow me to simply assign meaning to myself. I do this all the time with enumerations, but that will not allow me to do this with classes. Is there a way to implement in a convenient initializer using an instance of the class created in the implementation of the initializer?

Answer 1

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extension NSData {
    convenience init?(JSONObject: AnyObject) {
        do {
            let foo = try NSJSONSerialization.dataWithJSONObject(JSONObject, options: [])
            self.init(data: foo)
        }
        catch {
            return nil
        }
    }
}

/* Example usage */
let foo : AnyObject = ["Foo":"bar"]
let bar = NSData.init(JSONObject: foo)

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"... init". convenience ( ) - ( ). Swift Language Guide - - :

...

2

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3

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() , NSJSONSerialization.dataWithJSONObject(...) , , ( init(data:), ).

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. Swift Language Guide - Initialization - Failable Initializers. (convenience -> ... -> designated initializer) . rickster: s .

Answer 2

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