Pre-SIP: A New Type for Optionals and Error Handling (2)

[soronpo]

@odersky

For instance, here are suitable extension methods for map and flatMap:

  extension [A, E](x: A ? E)

    def map[B](f: A => B): B ? E = x match
      case Ok(y) => Ok(f(y))
      case Err(e) => Err(e)

    def flatMap[B](f: A => B ? E): B ? E = x match
      case Ok(y) => f(y)
      case Err(e) => Err(e)

I imagine these will be placed in Predef. This will cause two issues:

1. Due to erasure, it will collide with existing map and flatMap methods that the user may define. So if introduced in Predef, these will be need @targetType("scalaPredefMap"), @targetType("scalaPredefFlatMap"), etc.
2. Even if 1 is fixed, there is still the issue where extension methods with the same name do not work well due to shadowing. Relaxed extension methods (SIP 54) are not relaxed enough