On Sat, Mar 22, 2014 at 8:59 AM, Pascal Voitot Dev <
pascal.voitot....@gmail.com> wrote:
> The problem I was talking about is when you try to use typeclass converters
> and make them contravariant/covariant for input/output. Something like:
>
> Reader[-I, +O] { def read(i:I): O }
>
> Doing this, you soon have implicit collisions and philosophical concerns
> about what it means to serialize/deserialize a Parent class and a Child
> class...
>
You should (almost) never make a typeclass param contravariant. It's almost
certainly not what you want:
https://issues.scala-lang.org/browse/SI-2509
-- David
