Unlock Existential Types for All Protocols

Evolution Pitches
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85

Unfortunately, it can not be generic.

/// Represents an HTTP task.
public enum Task {
  case requestPlain
  
  case requestData(Data)
  
  /// A request body set with `Encodable` type
  case requestJSONEncodable(Encodable)
}

Task is used in different network providers, it is impossible to make it generic, such as Task<T>.
In case we use requestJSONEncodable(Encodable), we use type erased Encodable. But try encoder.encode(value) function needs a concrete Type, so type erasure struct is needed.

For more details, see Moya: GitHub - Moya/Moya: Network abstraction layer written in Swift.