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cats.evidence.Is and Scala 2.13 #2569

durban opened this Issue Oct 19, 2018 · 1 comment


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durban commented Oct 19, 2018

As far as I can tell, =:= in Scala 2.13 is very similar (identical?) in functionality to cats.evidence.Is. Would it make sense to revisit the decision regarding Is.unsafeFromPredef?

  • One thing is the unsafe prefix. Is it really unsafe? Especially now that in 2.13, it seems possible to write (A =:= B) => (A Is B) without any asInstanceOf.
  • The other (probably more important) is implicitness: if they're equivalent, maybe having an Is implicitly available when =:= is, would not be so bad.

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alexknvl commented Oct 22, 2018

It is not really unsafe. However, unless the support for 2.11 and 2.12 is dropped, it has to be implemented using coercion (asInstanceOf); having separate implementation for 2.12 and 2.13 would probably be undesirable in this particular case.

I think it would be nice to have it implicit.

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