Array of protocol type

Question

I have checked all answers about this problem on stackoverflow, but still can not figure out how to fix this. My model looks like this

protocol Commandable: Eq         


        

Answer 1

I think it can be easily done by introduction of your own CustomEquatable protocol.

protocol Commandable: CustomEquatable {
    var condition: String {get}
}

protocol CustomEquatable {
    func isEqual(to: CustomEquatable) -> Bool
}

Then, you objects have to conform to this protocol and additionally it should conform Equitable as well.

struct MoveCommand: Commandable, Equatable {
    let movingVector: CGRect
    let condition: String

    func isEqual(to: CustomEquatable) -> Bool {
        guard let rhs = to as? MoveCommand else { return false }

        return movingVector == rhs.movingVector && condition == rhs.condition
    }
}

struct RotateCommand: Commandable, Equatable {
    let side: CGFloat
    let condition: String

    func isEqual(to: CustomEquatable) -> Bool {
        guard let rhs = to as? RotateCommand else { return false }

        return side == rhs.side && condition == rhs.condition
    }
}

All you need to do now is connect your CustomEquatable protocol to Swift Equatable through generic extension:

extension Equatable where Self: CustomEquatable {

    static func ==(lhs: Self, rhs: Self) -> Bool {
        return lhs.isEqual(to: rhs)
    }
}

It's not a perfect solution, but now, you can store your objects in a array of protocol objects and use == operator with your objects as well. For example(I simplified objects a little bit):

let move = MoveCommand(movingVector: .zero, condition: "some")
let rotate = RotateCommand(side: 0, condition: "some")

var array = [Commandable]()
array.append(move)
array.append(rotate)  

let equal = (move == MoveCommand(movingVector: .zero, condition: "some"))
let unequal = (move == MoveCommand(movingVector: .zero, condition: "other"))
let unequal = (move == rotate) // can't do this, compare different types

PS. Using var on struct is not a good practice, especially for performance reasons.