Can't access members of protocol types

protocol-type-member.swift

public protocol MeasurementUnit {
    // If we have one of this unit, how many millimeters is it?
    class var asMillimeters: Double { get }
}
public class Inch : MeasurementUnit {
    public class var asMillimeters: Double {
	get {
            return 25.4
	}
    }
}

let unit: MeasurementUnit.Type = Inch.self

println("unit to mm = \(unit.asMillimeters)")

/* Yields:
protocol-type-member.swift:15:25: error: accessing members of protocol type value 'MeasurementUnit.Type' is unimplemented
*/

It would seem swift does not yet support protocol type properties or methods yet. In the meantime the next best thing would be to make it an instance variable, I guess?

public protocol MeasurementUnit {
  var asMillimeters: Double { get }
  init()
}

public class Inch: MeasurementUnit {
  public var asMillimeters: Double {
    get { return 25.4 }
  }

  public required init() {}
}

let unit: MeasurementUnit.Type = Inch.self
unit().asMillimeters

It's not great but it will work for me for now.

This is not fixed yet as of April 2015. So annoying. I need to implement the following:

protocol CloudStorable {
   class var classUrlString: String { get }
}

class DownloadTask<T: CloudStorable> {

   func execute() {
      var destinationUrl = "http://localhost:1234/" + T.classUrlString
      // this does not work, and I cannot simply make the property non-static
      // because I do not have an instance of CloudStorable before downloading.
   }
}

I'd also like to know how this works...

+1

"@objc protocol meas {
class var asm: Double{get}
}

class inc : meas {
class var asm: Double {
get {
return 25
}
}

}

let a = inc.self as meas.Type
let b:AnyClass = a as Any as AnyClass
b.asm"

Can you try this .I have made protocol to objc type, and did some downcasting. Please let me know if this worked

It seems you can access the static method as long as you declare the protocol using @objc and then cast the variable to AnyClass