The service variable in ViewController should be able to take every type that conforms to the RESTServiceType Protocol. But this produces a Swift Compiler Error.

ProtocolType.swift

import UIKit

protocol RESTServiceType {
    class func getData()
}

struct RESTService: RESTServiceType {
    static func getData() {
        println("Data")
    }
}

class ViewController {
    var service: RESTServiceType.Type = RESTService.self

    func viewDidLoad() {
        service.getData()
    }
}

ViewController().viewDidLoad()