jasper-m/implicitlogic

A simple toy project for playing around with some implicit resolution tricks

implicitlogic

This is a simple toy project for playing around with some implicit resolution tricks.

Examples

scala> import implicitlogic._
import implicitlogic._

scala> def stringIntSymbol[A](a: A)(implicit ev: (A <:< String) Or (A <:< Int) Or (A <:< Symbol)): A = a
stringIntSymbol: [A](a: A)(implicit ev: implicitlogic.Or[implicitlogic.Or[<:<[A,String],<:<[A,Int]],<:<[A,Symbol]])A

scala> stringIntSymbol(42)
res8: Int = 42

scala> stringIntSymbol("foo")
res9: String = foo

scala> stringIntSymbol('bar)
res10: Symbol = 'bar

scala> stringIntSymbol(42.5)
<console>:16: error: could not find implicit value for parameter ev: implicitlogic.Or[implicitlogic.Or[<:<[Double,String],<:<[Double,Int]],<:<[Double,Symbol]]
       stringIntSymbol(42.5)
                      ^

scala> def noAnyTypes[A](x: A, y: A)(implicit ev: Not[(AnyVal <:< A) Or (AnyRef <:< A)]) = List(x,y)
noAnyTypes: [A](x: A, y: A)(implicit ev: implicitlogic.Not[implicitlogic.Or[<:<[AnyVal,A],<:<[AnyRef,A]]])List[A]

scala> noAnyTypes(3, "foo")
<console>:16: error: ambiguous implicit values:
 both method makeNot in object Not of type [A]=> implicitlogic.Not[A]
 and method makeNotAmbig in object Not of type [A](implicit a: A)implicitlogic.Not[A]
 match expected type implicitlogic.Not[implicitlogic.Or[<:<[AnyVal,Any],<:<[AnyRef,Any]]]
       noAnyTypes(3, "foo")
                 ^

scala> noAnyTypes(BigInt(4), 7)
<console>:16: error: ambiguous implicit values:
 both method makeNot in object Not of type [A]=> implicitlogic.Not[A]
 and method makeNotAmbig in object Not of type [A](implicit a: A)implicitlogic.Not[A]
 match expected type implicitlogic.Not[implicitlogic.Or[<:<[AnyVal,Any],<:<[AnyRef,Any]]]
       noAnyTypes(BigInt(4), 7)
                 ^

scala> noAnyTypes(Some(5), None)
res23: List[Option[Int]] = List(Some(5), None)

scala> def noIntegralFractions[A](a: A)(implicit ev: Not[Integral[A] And Fractional[A]]): A = a
noIntegralFractions: [A](a: A)(implicit ev: implicitlogic.Not[implicitlogic.And[Integral[A],Fractional[A]]])A

The underlying values of And and Or can be accessed through their result attribute. Not obviously has no result. You can also use the aliases &&, || and !.

scala> val (numeric, ordering) = implicitly[Numeric[Int] && Ordering[Int]].result
numeric: Numeric[Int] = scala.math.Numeric$IntIsIntegral$@21d0366
ordering: Ordering[Int] = scala.math.Ordering$Int$@11507b97

scala> val Left(numeric) = implicitly[Numeric[Int] || Ordering[Int]].result
numeric: Numeric[Int] = scala.math.Numeric$IntIsIntegral$@21d0366

Xor is defined in function of And, Or and Not.

scala> implicitly[Numeric[Int] Xor Ordering[Int]]
<console>:15: error: could not find implicit value for parameter e: implicitlogic.Xor[Numeric[Int],Ordering[Int]]
       implicitly[Numeric[Int] Xor Ordering[Int]]
                 ^

scala> trait Foo[T]
defined trait Foo

scala> implicitly[Numeric[Int] Xor Foo[Int]]
res2: implicitlogic.Xor[Numeric[Int],Foo[Int]] = Xor(Left(scala.math.Numeric$IntIsIntegral$@60a53041))

scala> implicitly[Foo[Int] Xor Ordering[Int]]
res3: implicitlogic.Xor[Foo[Int],Ordering[Int]] = Xor(Right(scala.math.Ordering$Int$@69c31872))

There are also some helpful type aliases in the typehelpers object.