Expressing type inequality conditions in a simple estimate
import shapeless._
trait Something[T <: Something[T, R], R] {}
class Test[T <: Something[T, R], R, T1 <: Something[T1, _] <:!< T](t: T, t1: T1) {}
but i get:
type arguments [T1,?] do not conform to trait Something type parameter bounds [T <: Something[T,R],R]
Which makes sense, except that I expect this to work:
class Test1[T <: Something[T, R], R, T1 <: Something[T1, R1] <:!< T, R1](t: T, t1: T1)
But it asks for the same grade on T1 <: Something[T, R]
.
My point is that this class takes 4 type arguments, each pair describes a different descendant Something[T <: Something[T, R], R]
. Simple put, forced to T != T1
.
What is the correct way to do this?
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1 answer
General example
import shapeless._
class Foo[A, B](a: A, b: B)(implicit ev: A =:!= B)
val x = new Foo(1, "hello")
// x: Foo[Int,String] = Foo@4015d0b9
val y = new Foo(1, 2)
// error: ambiguous implicit values:
// both method neqAmbig1 in package shapeless of type [A]=> shapeless.=:!=[A,A]
// and method neqAmbig2 in package shapeless of type [A]=> shapeless.=:!=[A,A]
// match expected type shapeless.=:!=[Int,Int]
// new Foo(1, 2)
// ^
in your specific case
class Test[A, B, T <: Something[T, A], T1 <: Something[T1, B]](t: T, t1: T1)(implicit ev: T =:!= T1)
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