Type Properties in swift?

Question

In the Apple documentation for type properties the following code is given:

struct AudioChannel {
    static let thresholdLevel = 10
    static var maxInputLevelForAllChannels = 0
    var currentLevel: Int = 0 {
        didSet {
            if currentLevel > AudioChannel.thresholdLevel {
                // cap the new audio level to the threshold level
                currentLevel = AudioChannel.thresholdLevel
            }
            if currentLevel > AudioChannel.maxInputLevelForAllChannels {
                // store this as the new overall maximum input level
                AudioChannel.maxInputLevelForAllChannels = currentLevel
            }
        }
    }
}

The type properties are defined in a similar way to the "static" variables of the C language. In the example above, what would be the advantage of declaring type properties, and if they aren't declared what would be the effect or what difference would it make?

http://stackoverflow.com/questions/24217586/structure-vs-class-in-swift-language — Nikos M., Nov 30 '15 at 06:12
But it has given the difference between class & structure. Please can you give an answer to my question specifically — G.Abhisek, Nov 30 '15 at 06:16

score 3 · Accepted Answer · answered Nov 30 '15 at 07:10

Type variables, as the name implies, are variables for the whole type, as opposed to instance variables, which are variables for each of the instances.

That means, in the case of the code you posted, that every AudioChannel you create will have the same values for thresholdLevel and maxInputLevelForAllChannels. And when something changes those variables all instances will have access to the new values.

Type Properties in swift?

1 Answers1