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Provide CanEqual for Option (Option == None), Throwables, and other

See original GitHub issue

Minimized code

x match {
  case Some(value) =>
  case None =>
}

Output

[error] 129 |					case None =>
[error]     |					     ^^^^
[error]     |					     Values of types object None and Option[T] cannot be compared with == or !=.
[error]     |					     I found:
[error]     |
[error]     |					         CanEqual.canEqualOptions[T, U](/* missing */summon[CanEqual[T, U]])
[error]     |
[error]     |					     But no implicit values were found that match type CanEqual[T, U].

Expectation

CanEqual instance should come already defined for at the very least, the standard library. You have to strike a balance between versatility and usability.

As it is currently, -language:strictEquality is too cautious to be useful.

Issue Analytics

State:
Created a year ago
Comments:5 (4 by maintainers)

Top GitHub Comments

1reaction

oderskycommented, Jun 25, 2022

The problem is that the CanEqual instance would logically have to be in the companion object of Option. But we cannot touch the standard library for the time being, since we want to use 2.13.

At some point we need to decide that we will ship a Scala 3 specific standard library, and in that case CanEqual instances would be provided. Until then, I agree that -language:strictEquality is not useful and should be avoided.

0reactions

Kevin-Leecommented, Jul 8, 2022

@strelec Do you still have this problem? Are you using Scala 3.0.x? It should be fixed by #12419 and #13265 in Scala 3.1.0 and higher.

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