Unary operator definitions for custom types in Scala

Question

Tried running this code:

def ! : Int => Boolean = (p : Int => Boolean) => !p

Has a compilation error:

[error] value unary_! is not a member of Int => Boolean [error] def ! : Int => Boolean = (p : Int => Boolean) => !p

error is highlighted for "!p"

Shouldn't the compiler automatically figure out that the result of p is a Boolean ?

Thanks in advance

EDIT: Based on comments, tried the following also. Have accomplished my task using other methods, nonetheless, am trying to learn how to define an unary operator

def unary_! : Int => Boolean = (p : Int => Boolean) => !(p(_))

still getting a compiler error at "!(p(_))"

Unary ! for a custom type must be named unary_! as in the error. Your p takes an Int, so !p(42). — som-snytt
– som-snytt, Commented Jun 26, 2016 at 0:56
It's not at all clear what you are trying to accomplish. Could you be more specific about what you want this to do? — Joe Pallas
– Joe Pallas, Commented Jun 26, 2016 at 5:50
You're not calling p. So the ! isn't negating the return value of p, but p itself, and ! isn't an operator defined for functions. — The Archetypal Paul
– The Archetypal Paul, Commented Jun 26, 2016 at 7:01
For example github.com/scala/scala/blob/v2.12.0-M4/src/library/scala/math/… — som-snytt
– som-snytt, Commented Jun 26, 2016 at 13:59

som-snytt · Accepted Answer · 2016-06-26 14:08:19Z

Maybe you intend something like:

scala> class C(p: Int => Boolean) { def unary_! : Int => Boolean = !p(_) } defined class C scala> val c = new C(i => i < 0) c: C = C@4d9cad9d scala> (!c)(42) res0: Boolean = true

Very nice. Thanks much. Will have to figure out why this works & my attempts did not.

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