Packages

sealed abstract class Arbitrary[T] extends Serializable

Define an arbitrary generator for properties

The Arbitrary module defines implicit generator instances for common types.

The implicit definitions of Arbitrary provide type-directed Gens so they are available for properties, generators, or other definitions of Arbitrary.

ScalaCheck expects an implicit Arbitrary instance is in scope for Props that are defined with functions, like Prop.forAll and so on.

For instance, the definition for Arbitrary[Boolean] is used by Prop.forAll to automatically provide a Gen[Boolean] when one of the parameters is a Boolean:

Prop.forAll { (b: Boolean) =>
  b || !b
}

Thanks to Arbitrary, you don't need to provide an explicit Gen instance to Prop.forAll. For instance, this is unnecessary:

val genBool: Gen[Boolean] = Gen.oneOf(true,false)
Prop.forAll(genBool) { (b: Boolean) =>
  b || !b
}

Since an arbitrary Gen for Boolean is defined in Arbitrary, it can be summoned with Arbitrary.arbitrary in cases where you need to provide one explicitly:

val genBool: Gen[Boolean] = Arbitrary.arbitrary[Boolean]
val genSmallInt: Gen[Int] = Gen.choose(0, 9)
Prop.forAll(genBool, genSmallInt) { (b: Boolean, i: Int) =>
  i < 10 && b || !b
}

For a user-defined MyClass, writing the following requires that there exists an implicit Arbitrary[MyClass] instance:

Prop.forAll { (myClass: MyClass) =>
  ...
}

The implicit definition of Arbitrary[MyClass] would look like:

implicit val arbMyClass: Arbitrary[MyClass] = Arbitrary {
  ...
}

The factory method Arbitrary(...) expects a generator of type Gen[MyClass] then it will return an instance of Arbitrary[MyClass].

Source
Arbitrary.scala
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Abstract Value Members

  1. abstract def arbitrary: Gen[T]

Concrete Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean
    Definition Classes
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  4. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  5. def clone(): AnyRef
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    protected[lang]
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    @throws( ... ) @native()
  6. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  7. def equals(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  8. def finalize(): Unit
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    protected[lang]
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    @throws( classOf[java.lang.Throwable] )
  9. final def getClass(): Class[_]
    Definition Classes
    AnyRef → Any
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    @native()
  10. def hashCode(): Int
    Definition Classes
    AnyRef → Any
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    @native()
  11. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  12. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  13. final def notify(): Unit
    Definition Classes
    AnyRef
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    @native()
  14. final def notifyAll(): Unit
    Definition Classes
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    @native()
  15. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  16. def toString(): String
    Definition Classes
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  17. final def wait(): Unit
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    @throws( ... )
  18. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
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    @throws( ... )
  19. final def wait(arg0: Long): Unit
    Definition Classes
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    @throws( ... ) @native()

Inherited from Serializable

Inherited from Serializable

Inherited from AnyRef

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