Calculate complement of a predicate

Question
1

When I have to pass a predicate to a function, such as filter and I want the negative of the predicate, sometimes the function includes a cousin such as filterNot, but if it doesn’t, I’d like to complement the predicate. it is of course easy enough just to inline the complementation such as data.filter(p => !predicate(p)), but it seems to me there should already be such a function. I searched for Function.complement and predicate.complement but didn’t find such.

Does it already exist in the standard library?

I’m not sure how I’d write it myself in the general case.

2

You can further reduce the inlined version with underscore syntax, which would almost always be good enough for me:

data.filter(!predicate(_))

A naive stab at a generic complement operator:

implicit class ComplementablePredicate[T](val f: T => Boolean) extends AnyVal {
  def unary_! : T => Boolean = f.andThen(!_)
}

val p = (_: String).isEmpty
println(Seq("a", "", "b").filter(!p))

Best regards,
Patrick

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