Getting static variables from a string

Question

I have the following class that describes a country:

class Country: NSObject {

    public var name: String

    static let england = Country(name: "England")
    static let scotland = Country(name: "Scotland")
    static let allCountries = [england, scotland]

    init(name: String) {
        self.name = name
        super.init()
    }

    convenience init?(named name: String) {
        guard let country = Country.allCountries.filter( { $0.name == name } ).first else { return nil }
        self.init(name: country.name)
    }

}

To get the constant Country.england, I would use:

let england = Country.england

However, I want to be able to get this constant from a String using convenience init?(named name: String) as follows:

let england = Country(named: "England")

This seems a little clunky and this code initialises a new "england" instance rather than taking the static one.

Is there a more Swifty way of doing this? Ideally I'd like to just let self = country in the convenience init?(named name: String) function, but I get the error cannot assign to value: 'self' is immutable.

Thanks for any help.

Pro tip - use .first(where: { $0.name == name } ) rather than .filter( { $0.name == name } ).first — Ashley Mills
– Ashley Mills, Commented Sep 3, 2018 at 9:34

Ashley Mills · Accepted Answer · 2018-09-03 09:42:18Z

3

If your Country only has a name then you would be better off using an enum…

enum Country: String, CaseIterable {
    case england = "England"
    case scotland = "Scotland"
}

Country(rawValue: "Scotland") // Optional(scotland)
Country(rawValue: "Wales")    // nil

Note CaseIterable is Swift 4.2+ but allows you to write Country.allCases

Country.allCases  // [england, scotland]

edited Sep 3, 2018 at 9:42

answered Sep 3, 2018 at 9:37

Ashley Mills

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1 Comment

ajrlewis Over a year ago

Thanks for your suggestion. The original post is more of a minimal working example. The class is more complicated than just having one variable.

Sweeper · Accepted Answer · 2018-09-03 09:45:11Z

2

What about writing a named factory method instead?

static func named(_ name: String) -> Country? {
    return Country.allCountries.first(where: { $0.name == name } )
}

// usage:
let england = Country.named("England")!

The initializer approach could be used if Country were a struct:

struct Country {

    public var name: String

    static let england = Country(name: "England")
    static let scotland = Country(name: "Scotland")
    static let allCountries = [england, scotland]

    init(name: String) {
        self.name = name
    }

    init?(named name: String) {
        guard let country = Country.allCountries.filter( { $0.name == name } ).first else { return nil }
        self = country
    }

}

edited Sep 3, 2018 at 9:45

answered Sep 3, 2018 at 9:39

Sweeper

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4 Comments

ajrlewis Over a year ago

Thanks, I was leaning towards this being the better way, but it would look nicer to initialiser it rather than call a class function in my opinion...

Sweeper Over a year ago

@AlexJ.R.Lewis You could use an initialiser if Country were a struct. See the edit.

Ashley Mills Over a year ago

That was my next question - does it need to inherit from NSObject and does it need to be a `class?

ajrlewis Over a year ago

@AshleyMills I'll look into structs. Perhaps it doesn't need to inherit from NSObject. Country just needs to be equatable and have a bunch of UI* objects.

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