Imported From: https://issues.scala-lang.org/browse/SI-5426?orig=1
Reporter: Maciej Pilichowski (macias)
Affected Versions: 2.9.1

@paulp said:
Notice it warns the other way:

scala> println(y == x)
<console>:10: warning: comparing values of types Int and Some[Int] using `==' will always yield false
              println(y == x)
                        ^

a) is not going to happen, equals must be symmetric. b) is not going to happen either. A warning might be possible, but it's harder than it looks to warn where you want to without creating spurious warnings elsewhere.

@paulp said:
147e9eaf38

Maciej Pilichowski (macias) said:
ad.a) it could be symmetric with no problem

But if 2.10 will fix this, it is OK with me.

@paulp said:
If Some("a") == "a', how do you propose to modify final class String such that "a" == Some("a") ? If you think equals calls can be intercepted selectively, there is ("a": Object) == (Some("a"): Object). If you think we would rewrite every equals call to achieve this end, there is still a whole universe of java code we don't compile but must interoperate with. It is not no problem. (This is before getting to the fact that even if it were easy and imposed no cost, we wouldn't do it because it isn't true: Some(x) is not x.)

Maciej Pilichowski (macias) said:
I got idea, you already have equality check, only evaluating to false instead of true (after all it has to be defined somewhere, right?). I wouldn't worry about Java, because the problem is in Scala, Java has different rules and "A op B" can have different meaning in Java and Scala. "Some is not x." -- depends on perception, I am not saying it IS x, I am saying it is equal to x. "0.9(9)" IS not 1, but it is equal to 1. You can think of Option as -- solid value or nothing (None). Some(X) is representation of solid value. And besides what benefit is with evaluation to false? None, you have to make the code longer -- and Scala was supposed to cut unnecessary code. So you have to write "if (x.isDefined && x.get==y) ..." instead of just "if (x==y) ..."

@retronym said:
Best to drift this over to the mailing list [scala-debate]; here isn't the right forum. BTW, if (x == Some\(y)) ... ain't so bad..

@SethTisue said (edited on Jul 11, 2012 10:07:18 PM UTC):
re x == Some(y), see #6064

val seq = Seq(Some(5))
seq.find(_ == 5)

Do not warn if the comparison is within a Seq

Is there a compiler flag for this?

@avbhandaru you can ask on https://users.scala-lang.org or https://discord.com/invite/scala