Applying Generics to Variables and Functions - Swift

问题

I'm trying to use generics in swift in order to initialise variables within my Vector3D class. However, upon assigning the protocol 'Number' to my variable (to make it either a Double or Float) I get the following error:

Protocol 'Number' can only be used as a generic constraint because it has Self or associated type requirements

public protocol Number {
    func +(l: Self, r: Self) -> Self
}    
extension Double : Number {}
extension Float  : Number {}


class Vector3D: NSObject {

    var xCord: Number
    var yCord: Number
    var zCord: Number


    func Vector3D(x: [Number], y: [Number], z: [Number]) {
        self.xCord = x
        self.yCord = y
        self.zCord = z
    }
}

My questions is then, how do you apply generics to variables in swift and in functions?

回答1:

You can't add generics to variables in Swift as already shown in this answer, but you can add generics to a function like that:

func swapTwoValues<T>(inout a:T, inout b:T){
  let temporaryA = a
  a = b
  b = temporaryA
}

Check the apple Documentation.

回答2:

The generic is created here <T>. It's like a variable for Types. You can change the T to anything you want as long as it's not used as a Type somewhere. The constraint bit is : Number. It constraints the type of T to the types that adhere to the Number Protocol.

func Vector3D<T: Number>(x: [T], y: [T], z: [T]) {
    self.xCord = x
    self.yCord = y
    self.zCord = z
}

As stated in the other answer, Variables and Constants cannot be of type Generic.

来源：https://stackoverflow.com/questions/28160345/applying-generics-to-variables-and-functions-swift

标签

ios

generics

swift

protocols

nsobject