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