Wrong generic use of ObservableArray/MutableObservableArray?

[vietstone-ng]

Hello,

To demonstrate my generic use, I write 2 pieces of code as below.

1. This piece results in an error at the 'return' statement:

import Foundation
import Bond

protocol MyProtocolType { }

struct MyValueType: MyProtocolType { }

class MyCustomClass {
  static let singleton = MyCustomClass()
  
  private init() { }
  
  func getList() -> ObservableArray<MyProtocolType> {
    let list = MutableObservableArray([MyValueType()])
    return list.readOnlyView
  }
}

2. This piece of code runs ok:

import Foundation
import Bond

protocol MyProtocolType { }

struct MyValueType: MyProtocolType { }

class MyCustomClass {
  static let singleton = MyCustomClass()
  
  private init() { }
  
  func getList() -> ObservableArray<MyValueType> {
    let list = MutableObservableArray([MyValueType()])
    return list.readOnlyView
  }
}

The difference is at the function's return type: ObservableArray<MyProtocolType> vs ObservableArray<MyValueType>.

I think the correct syntax for generic usage is the 1st one, but Xcode reports error with it. So I need to change to the 2nd one.

I don't understand it. Or is my syntax incorrect? If you know the reason, please point me out.

Thank you!