Why can't I initialize a static variable by calling a static function in Swift?

Question

It is my understanding that as of Xcode 6.3 / Swift 1.2, I can use static variables and methods inside of a class. However, the compiler doesn't like it when I try to initialize a static variable by calling a static function (I get the error 'Use of unresolved identifier getDefaultString' in the example below). Here is a snippet that demonstrates my problem:

import Foundation

public class Settings {
    private static var _bundle = NSBundle.mainBundle()
    static func getDefaultString(key: String) -> String {
        return _bundle.objectForInfoDictionaryKey(key) as! String
    }

    private static var _server = getDefaultString("DefaultServer")
    public class var server: String {
        get { return _server }
        set { _server = newValue }
    }
}

Can someone help me understand why I can't do this?

Does it work if you use private static var _server = Settings.getDefaultString("DefaultServer")? — NobodyNada
– NobodyNada, Commented Jun 15, 2015 at 20:40

0x416e746f6e · Accepted Answer · 2015-06-15 21:07:27Z

14

This should work:

private static var _server = Settings.getDefaultString("DefaultServer")

I do not know exactly why, it seems that there is some sort of an assumption in the play that a method without type qualified in front of it is an instance method. But that does not fully work as well. E.g. this produces interesting result in playground:

    class Foo {

        static func initFoo() -> String {
            return "static"
        }

        func initFoo() -> String {
            return "instance"
        }

        static var foo: String = initFoo()

    }

    Foo.foo

... no need to qualify type in front of initFoo(), but still the static one is picked up. A minor bug probably.

edited Jun 15, 2015 at 21:07

answered Jun 15, 2015 at 20:56

0x416e746f6e

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Comments

bshirley · Accepted Answer · 2016-01-28 21:10:23Z

You are forcing an unwrap of a possible (and actual) nil object.

return _bundle.objectForInfoDictionaryKey(key) as! String

NSBundle's objectForInfoDictionaryKey can return nil – its declaration:

func objectForInfoDictionaryKey(key: String) -> AnyObject?

my edit, as a playground:

import Foundation

class Settings {
    private static var _bundle = NSBundle.mainBundle()
    static func getDefaultString(key: String) -> String? {
        return _bundle.objectForInfoDictionaryKey(key) as? String
    }

    private static var _server = Settings.getDefaultString("DefaultServer")

    class var server: String? {
        get { return _server }
        set { _server = newValue }
    }
}

Settings.server

You can, of course, fallback from a nil in some other fashion if you prefer.

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