Confusion when trying to create a Protocol extension constrained based on RawRepresentable.RawType

Using Swift
1

In the code pasted below, the compiler generates the following error:

Type 'Position' does not conform to protocol 'RegistryCodable'

import Cocoa

struct IntBuffer {}
struct StringBuffer {}

protocol RegistryCodable {
  associatedtype BufferType
  
  init(registryBuffer: BufferType)
}

extension RegistryCodable where Self: RawRepresentable, Self.RawValue == Int {
  init(registryBuffer: IntBuffer) { /* A default implementation. */ }
}

extension RegistryCodable where Self: RawRepresentable, Self.RawValue == String {
  init(registryBuffer: StringBuffer) { /* A default implementation. */ }
}

enum Position: String, RegistryCodable {
  case top
  case bottom
}

Why is this default implementaiton not considered sufficient for making Position conform to RegistryCodable? Is there a way to make it?

I have numerous enums that are RawRepresentable. Something that is RawRepresentable, in this application, can be easily encoded and decoded into a type of Registry. I was hoping I could avoid having to define an implementation for each enum by using an extension as shown above, but that doesn't seem to be the case.

2

I don't know if there is a technical reason why the thing you wrote isn't sufficient, but you can help the compiler by explicitly writing what is your buffer type

enum Position: String, RegistryCodable {
  typealias BufferType = StringBuffer
  case top
  case bottom
}