Fail Compilation for Comparison of Different Types?

[Kevin Meredith]

Is there a scalac flag that will fail this compilation?

$scala "-Xfatal-warnings"

scala> val x: Seq[Option[Int]] = Seq( Some(1) )

x: Seq[Option[Int]] = List(Some(1))

// comparing Option[Int] to Int 

scala> x.map(_ == 4) 

res0: Seq[Boolean] = List(false)

Thanks,

Kevin

[Dennis Haupt]

you could use intellij (it has an inspection for this)

or you could define your own equals that only works on the same types using an implicit

 

Gesendet: Sonntag, 02. August 2015 um 02:15 Uhr
Von: "Kevin Meredith" <kevin.m....@gmail.com>
An: scala-user <scala...@googlegroups.com>
Betreff: [scala-user] Fail Compilation for Comparison of Different Types?

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[Oliver Ruebenacker]

     Hello,

  You can only proof that the comparison is never true if one of the types is final or sealed. It can be proven for the given example, because as it happens Int is final and Option is sealed. Below, Scala says "they will most likely never compare equal". Well, it didn't say "absolutely never".

[oruebenacker@localhost ~]$ scala
Welcome to Scala version 2.11.7 (OpenJDK 64-Bit Server VM, Java 1.8.0_51).
Type in expressions to have them evaluated.
Type :help for more information.

scala> trait A
defined trait A

scala> trait B
defined trait B

scala> class C extends A with B
defined class C

scala> val c = new C
c: C = C@57fa26b7

scala> val a: A = c
a: A = C@57fa26b7

scala> val b: B = c
b: B = C@57fa26b7

scala> a == b
<console>:17: warning: A and B are unrelated: they will most likely never compare equal
       a == b
         ^
res0: Boolean = true

     Best, Oliver

--

Oliver Ruebenacker

Senior Software Engineer, Diabetes Portal, Broad Institute