Type-safe contains

Language Design
16

Yes. Wartremover has a specific rules (“warts”) against inferred Any, AnyVal, JavaSerializable, and Product , which in combination can catch a lot of these. (Though as discussed above, the general problem exists for any common traits).

For Scalafix 0.8.0-RC1 that just came out I wrote a rule yesterday called NoInfer to catch specific inference, and blogged about it as stricter Scala with -Xlint, -Xfatal-warnings, and Scalafix.

[info] Running scalafix on 2 Scala sources
[error] /Users/eed3si9n/work/quicktest/noinfer/Main.scala:7:3: error: [NoInfer.Serializable] Serializable was inferred, but it's forbidden by NoInfer
[error]   List(Animal()).contains("1")
[error]   ^^^^^^^^^^^^^^^^^^^^^^^
[error] /Users/eed3si9n/work/quicktest/noinfer/Main.scala:8:3: error: [NoInfer.any2stringadd] any2stringadd was inferred, but it's forbidden by NoInfer
[error]   Option(1) + "what"
[error]   ^^^^^^^^^
[error] /Users/eed3si9n/work/quicktest/noinfer/Main.scala:9:3: error: [NoInfer.Product] Product was inferred, but it's forbidden by NoInfer
[error]   List(Nil).contains(Some(1))
[error]   ^^^^^^^^^^^^^^^^^^
[error] /Users/eed3si9n/work/quicktest/noinfer/Main.scala:9:3: error: [NoInfer.Serializable] Serializable was inferred, but it's forbidden by NoInfer
[error]   List(Nil).contains(Some(1))
[error]   ^^^^^^^^^^^^^^^^^^
[error] (Compile / scalafix) scalafix.sbt.ScalafixFailed: LinterError

In terms of the short-term, reducing foot-guns, I think Paul’s (implicit ev: T <:< T1) trick is worth considering.

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