Scala中类型不相等的证据 [英] Evidence that types are not equal in Scala

问题描述

是否有任何方法可以约束方法，以便仅在证明两种类型不相等时才有意义?

Is there any way to constraint a method so that it only makes sense if two types are proved not to be equal?

trait Something[A, B] {
  // I can only be called if type A is the same as type B
  def ifEqual(implicit ev: A =:= B)

  // Now I cannot be called if type A is proven to be the same as type B
  def ifNotEqual(implicit ev: A ??? B)
}

推荐答案

是.来自不变形，

// Type inequalities
trait =:!=[A, B] 

implicit def neq[A, B] : A =:!= B = new =:!=[A, B] {}
implicit def neqAmbig1[A] : A =:!= A = ???
implicit def neqAmbig2[A] : A =:!= A = ???

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