org.scalautils

TypeCheckedTripleEquals

trait TypeCheckedTripleEquals extends LowPriorityTypeCheckedConstraint

Provides === and !== operators that return Boolean, delegate the equality determination to an Equality type class, and require the types of the two values compared to be in a subtype/supertype relationship.

Recommended Usage: Trait TypeCheckedTripleEquals is useful (in both production and test code) when you need determine equality for a type of object differently than its equals method—either you can't change the equals method, or the equals method is sensible generally, but you're in a special situation where you need something else—and/or you want to enforce at compile-time that the types of the compared values are in a subtype/supertype relationship.

This trait is the strictest of the three triple equals traits, enforcing a stronger constraint than both TripleEquals (the most lenient) and ConversionCheckedTripleEquals (the middle ground). If TripleEquals is mixed in or imported, the === can be used with any two types and still compile. If TypeCheckedTripleEquals is mixed in or imported, however, only types in a subtype or supertype relationship with each other (including when both types are exactly the same) will compile. ConversionCheckedTripleEquals is slightly more accomodating, because in addition to compiling any use of === that will compile under TypeCheckedTripleEquals, it will also compile type types that would be rejected by TypeCheckedTripleEquals, so long as an implicit conversion (in either direction) from one type to another is available.

For example, under TypeCheckedTripleEquals, the following use of === will not compile, because Int and Long are not in a subtype/supertype relationship. (I.e., Int is not a subtype or supertype of Long):

scala> import org.scalautils._
import org.scalautils._

scala> import TypeCheckedTripleEquals._ import TypeCheckedTripleEquals._

scala> 1 === 1L <console>:14: error: types Int and Long do not adhere to the equality constraint selected for the === and !== operators; they must either be in a subtype/supertype relationship, or, if ConversionCheckedTripleEquals is in force, implicitly convertible in one direction or the other; the missing implicit parameter is of type org.scalautils.EqualityConstraint[Int,Long] 1 === 1L ^

Trait TypeCheckedTripleEquals rejects types Int and Long because they are not directly related via subtyping. However, an implicit widening conversion from Int to Long does exist (imported implicitly from scala.Predef), so ConversionCheckedTripleEquals will allow it:

scala> import ConversionCheckedTripleEquals._
import ConversionCheckedTripleEquals._

scala> 1 === 1L res1: Boolean = true

The implicit conversion can go in either direction: from the left type to the right type, or vice versa. In the above expression the implicit conversion goes from left to right (the Int on the left to the Long on the right). It also works the other way:

scala> 1L === 1
res2: Boolean = true

This trait will override or hide implicit methods defined by its sibling traits, TripleEquals or TypeCheckedTripleEquals, and can therefore be used to temporarily turn on or off conversion checking in a limited scope. Here's an example, in which TypeCheckedTripleEquals will cause a compiler error:

import org.scalautils._
import TypeCheckedTripleEquals._

object Example {

def cmp(a: Int, b: Long): Int = { if (a === b) 0 // This line won't compile else if (a < b) -1 else 1 }

def cmp(s: String, t: String): Int = { if (s === t) 0 else if (s < t) -1 else 1 } }

Because Int and Long are not in a subtype/supertype relationship, comparing 1 and 1L in the context of TypeCheckedTripleEquals will generate a compiler error:

Example.scala:9: error: types Int and Long do not adhere to the equality constraint selected for
the === and !== operators; they must either be in a subtype/supertype relationship, or, if
ConversionCheckedTripleEquals is in force, implicitly convertible in one direction or the other;
the missing implicit parameter is of type org.scalautils.EqualityConstraint[Int,Long]
    if (a === b) 0      // This line won't compile
          ^
one error found

You can “relax” the type checking (i.e., by additionally allowing implicitly convertible types) locally by importing the members of ConversionCheckedTripleEquals in a limited scope:

package org.scalautils.examples.conversioncheckedtripleequals

import org.scalautils._
import TypeCheckedTripleEquals._

object Example {

  def cmp(a: Int, b: Long): Int = {
    import ConversionCheckedTripleEquals._
    if (a === b) 0
    else if (a < b) -1
    else 1
  }

 def cmp(s: String, t: String): Int = {
   if (s === t) 0
   else if (s < t) -1
   else 1
 }
}

With the above change, the Example.scala file compiles fine. Conversion checking is enabled only inside the first cmp method that takes an Int and a Long. TypeCheckedTripleEquals is still enforcing its type constraint, for example, for the s === t expression in the other overloaded cmp method that takes strings.

Because the methods in ConversionCheckedTripleEquals (and its siblings) override all the methods defined in supertype EqualityConstraints, you can achieve the same kind of nested tuning of equality constraints whether you mix in traits, import from companion objects, or use some combination of both.

In short, you should be able to select a primary constraint level via either a mixin or import, then change that in nested scopes however you want, again either through a mixin or import, without getting any implicit conversion ambiguity. The innermost constraint level in scope will always be in force.

An alternative way to solve an unwanted compiler error caused by an over-zealous equality type constraint is to convert one side or the other to type Any. Because Any is a supertype of everything, any level of equality type constraint will be satisfied. The AsAny trait offers a convenient syntax, the asAny method, for this purpose:

scala> import org.scalautils._
import org.scalautils._

scala> import TypeCheckedTripleEquals._ import TypeCheckedTripleEquals._

scala> import AsAny._ import AsAny._

scala> 1 === 1L >console>:17: error: types Int and Long do not adhere to the equality constraint selected for the === and !== operators; they must either be in a subtype/supertype relationship, or, if ConversionCheckedTripleEquals is in force, implicitly convertible in one direction or the other; the missing implicit parameter is of type org.scalautils.EqualityConstraint[Int,Long] 1 === 1L ^

scala> 1 === 1L.asAny res1: Boolean = true

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  1. TypeCheckedTripleEquals
  2. LowPriorityTypeCheckedConstraint
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Value Members

  1. def != (arg0: AnyRef): Boolean

    Attributes
    final
    Definition Classes
    AnyRef
  2. def != (arg0: Any): Boolean

    Attributes
    final
    Definition Classes
    Any
  3. def !== [T] (right: Interval[T]): TripleEqualsInvocationOnInterval[T]

    Returns a TripleEqualsInvocationOnInterval[T], given an Interval[T], to facilitate the “<left> should !== (<pivot> +- <tolerance>)” syntax of Matchers.

    Returns a TripleEqualsInvocationOnInterval[T], given an Interval[T], to facilitate the “<left> should !== (<pivot> +- <tolerance>)” syntax of Matchers.

    right

    the Interval[T] against which to compare the left-hand value

    returns

    a TripleEqualsInvocationOnInterval wrapping the passed Interval[T] value, with expectingEqual set to false.

    Definition Classes
    EqualityConstraints
  4. def !== (right: Null): TripleEqualsInvocation[Null]

    Returns a TripleEqualsInvocation[Null], given a null reference, to facilitate the “<left> should !== null” syntax of Matchers.

    Returns a TripleEqualsInvocation[Null], given a null reference, to facilitate the “<left> should !== null” syntax of Matchers.

    right

    a null reference

    returns

    a TripleEqualsInvocation wrapping the passed null value, with expectingEqual set to false.

    Definition Classes
    EqualityConstraints
  5. def !== [T] (right: T): TripleEqualsInvocation[T]

    Returns a TripleEqualsInvocation[T], given an object of type T, to facilitate the “<left> should !== <right>” syntax of Matchers.

    Returns a TripleEqualsInvocation[T], given an object of type T, to facilitate the “<left> should !== <right>” syntax of Matchers.

    right

    the right-hand side value for an equality assertion

    returns

    a TripleEqualsInvocation wrapping the passed right value, with expectingEqual set to false.

    Definition Classes
    EqualityConstraints
  6. def ## (): Int

    Attributes
    final
    Definition Classes
    AnyRef → Any
  7. def == (arg0: AnyRef): Boolean

    Attributes
    final
    Definition Classes
    AnyRef
  8. def == (arg0: Any): Boolean

    Attributes
    final
    Definition Classes
    Any
  9. def === [T] (right: Interval[T]): TripleEqualsInvocationOnInterval[T]

    Returns a TripleEqualsInvocationOnInterval[T], given an Interval[T], to facilitate the “<left> should === (<pivot> +- <tolerance>)” syntax of Matchers.

    Returns a TripleEqualsInvocationOnInterval[T], given an Interval[T], to facilitate the “<left> should === (<pivot> +- <tolerance>)” syntax of Matchers.

    right

    the Interval[T] against which to compare the left-hand value

    returns

    a TripleEqualsInvocationOnInterval wrapping the passed Interval[T] value, with expectingEqual set to true.

    Definition Classes
    EqualityConstraints
  10. def === (right: Null): TripleEqualsInvocation[Null]

    Returns a TripleEqualsInvocation[Null], given a null reference, to facilitate the “<left> should === null” syntax of Matchers.

    Returns a TripleEqualsInvocation[Null], given a null reference, to facilitate the “<left> should === null” syntax of Matchers.

    right

    a null reference

    returns

    a TripleEqualsInvocation wrapping the passed null value, with expectingEqual set to true.

    Definition Classes
    EqualityConstraints
  11. def === [T] (right: T): TripleEqualsInvocation[T]

    Returns a TripleEqualsInvocation[T], given an object of type T, to facilitate the “<left> should === <right>” syntax of Matchers.

    Returns a TripleEqualsInvocation[T], given an object of type T, to facilitate the “<left> should === <right>” syntax of Matchers.

    right

    the right-hand side value for an equality assertion

    returns

    a TripleEqualsInvocation wrapping the passed right value, with expectingEqual set to true.

    Definition Classes
    EqualityConstraints
  12. def asInstanceOf [T0] : T0

    Attributes
    final
    Definition Classes
    Any
  13. def clone (): AnyRef

    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
  14. def conversionCheckedEqualityConstraint [A, B] (implicit equalityOfA: Equality[A], cnv: (B) ⇒ A): EqualityConstraint[A, B]

    Provides an EqualityConstraint[A, B] class for any two types A and B, enforcing the type constraint that B is implicitly convertible to A, given an implicit Equality[A].

    Provides an EqualityConstraint[A, B] class for any two types A and B, enforcing the type constraint that B is implicitly convertible to A, given an implicit Equality[A].

    The implicitly passed Equality[A] must be used to determine equality by the returned EqualityConstraint's areEqual method.

    This method is overridden and made implicit by subtraits ConversionCheckedTripleEquals) and ConversionCheckedLegacyTripleEquals, and overriden as non-implicit by the other subtraits in this package.

    equalityOfA

    an Equality[A] type class to which the EqualityConstraint.areEqual method will delegate to determine equality.

    cnv

    an implicit conversion from B to A

    returns

    an EqualityConstraint[A, B] whose areEqual method delegates to the areEqual method of the passed Equality[A].

    Definition Classes
    TypeCheckedTripleEqualsEqualityConstraints
  15. implicit def convertToCheckingEqualizer [T] (left: T): CheckingEqualizer[T]

    Convert to an CheckingEqualizer that provides === and !== operators that result in Boolean and enforce a type constraint.

    Convert to an CheckingEqualizer that provides === and !== operators that result in Boolean and enforce a type constraint.

    This method is overridden and made implicit by subtraits TypeCheckedTripleEquals and ConversionCheckedTripleEquals, and overriden as non-implicit by the other subtraits in this package.

    left

    the object whose type to convert to CheckingEqualizer.

    Attributes
    implicit
    Definition Classes
    TypeCheckedTripleEqualsEqualityConstraints
  16. def convertToEqualizer [T] (left: T): Equalizer[T]

    Convert to an Equalizer that provides === and !== operators that result in Boolean and enforce no type constraint.

    Convert to an Equalizer that provides === and !== operators that result in Boolean and enforce no type constraint.

    This method is overridden and made implicit by subtrait TripleEquals and overriden as non-implicit by the other subtraits in this package.

    left

    the object whose type to convert to Equalizer.

    Definition Classes
    TypeCheckedTripleEqualsEqualityConstraints
  17. def convertToLegacyCheckingEqualizer [T] (left: T): LegacyCheckingEqualizer[T]

    Convert to a LegacyCheckingEqualizer that provides === and !== operators that result in Option[String] and enforce a type constraint.

    Convert to a LegacyCheckingEqualizer that provides === and !== operators that result in Option[String] and enforce a type constraint.

    This method is overridden and made implicit by subtraits TypeCheckedLegacyTripleEquals and ConversionCheckedLegacyTripleEquals, and overriden as non-implicit by the other subtraits in this package.

    left

    the object whose type to convert to LegacyCheckingEqualizer.

    Definition Classes
    TypeCheckedTripleEqualsEqualityConstraints
  18. def convertToLegacyEqualizer [T] (left: T): LegacyEqualizer[T]

    Convert to a LegacyEqualizer that provides === and !== operators that result in Option[String] and enforce no type constraint.

    Convert to a LegacyEqualizer that provides === and !== operators that result in Option[String] and enforce no type constraint.

    This method is overridden and made implicit by subtrait LegacyTripleEquals and overriden as non-implicit by the other subtraits in this package.

    left

    the object whose type to convert to LegacyEqualizer.

    Definition Classes
    TypeCheckedTripleEqualsEqualityConstraints
  19. implicit def defaultEquality [A] : Equality[A]

    Return an Equality[A] for any type A that determines equality via the == operator on type A.

    Return an Equality[A] for any type A that determines equality via the == operator on type A.

    returns

    a DefaultEquality for type A

    Attributes
    implicit
    Definition Classes
    TypeCheckedTripleEqualsEqualityConstraints
  20. def eq (arg0: AnyRef): Boolean

    Attributes
    final
    Definition Classes
    AnyRef
  21. def equals (arg0: Any): Boolean

    Definition Classes
    AnyRef → Any
  22. def finalize (): Unit

    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
  23. def getClass (): java.lang.Class[_]

    Attributes
    final
    Definition Classes
    AnyRef → Any
  24. def hashCode (): Int

    Definition Classes
    AnyRef → Any
  25. def isInstanceOf [T0] : Boolean

    Attributes
    final
    Definition Classes
    Any
  26. def lowPriorityConversionCheckedEqualityConstraint [A, B] (implicit equalityOfB: Equality[B], cnv: (A) ⇒ B): EqualityConstraint[A, B]

    Provides an EqualityConstraint[A, B] class for any two types A and B, enforcing the type constraint that A is implicitly convertible to B, given an implicit Equality[A].

    Provides an EqualityConstraint[A, B] class for any two types A and B, enforcing the type constraint that A is implicitly convertible to B, given an implicit Equality[A].

    The implicitly passed Equality[A] must be used to determine equality by the returned EqualityConstraint's areEqual method.

    This method is overridden and made implicit by subtraits LowPriorityConversionCheckedConstraint (extended by ConversionCheckedTripleEquals), and LowPriorityConversionCheckedLegacyConstraint (extended by ConversionCheckedLegacyTripleEquals), and overriden as non-implicit by the other subtraits in this package.

    cnv

    an implicit conversion from A to B

    returns

    an EqualityConstraint[A, B] whose areEqual method delegates to the areEqual method of the passed Equality[A].

    Definition Classes
    TypeCheckedTripleEqualsEqualityConstraints
  27. implicit def lowPriorityTypeCheckedEqualityConstraint [A, B] (implicit equalityOfA: Equality[A], ev: <:<[A, B]): EqualityConstraint[A, B]

    Provides an EqualityConstraint[A, B] class for any two types A and B, enforcing the type constraint that A must be a subtype of B, given an implicit Equality[A].

    Provides an EqualityConstraint[A, B] class for any two types A and B, enforcing the type constraint that A must be a subtype of B, given an implicit Equality[A].

    The implicitly passed Equality[A] must be used to determine equality by the returned EqualityConstraint's areEqual method.

    This method is overridden and made implicit by subtraits LowPriorityTypeCheckedConstraint (extended by TypeCheckedTripleEquals), and LowPriorityTypeCheckedLegacyConstraint (extended by TypeCheckedLegacyTripleEquals), and overriden as non-implicit by the other subtraits in this package.

    equalityOfA

    an Equality[A] type class to which the EqualityConstraint.areEqual method will delegate to determine equality.

    ev

    evidence that A is a subype of B

    returns

    an EqualityConstraint[A, B] whose areEqual method delegates to the areEqual method of the passed Equality[A].

    Attributes
    implicit
    Definition Classes
    LowPriorityTypeCheckedConstraintEqualityConstraints
  28. def ne (arg0: AnyRef): Boolean

    Attributes
    final
    Definition Classes
    AnyRef
  29. def notify (): Unit

    Attributes
    final
    Definition Classes
    AnyRef
  30. def notifyAll (): Unit

    Attributes
    final
    Definition Classes
    AnyRef
  31. def synchronized [T0] (arg0: ⇒ T0): T0

    Attributes
    final
    Definition Classes
    AnyRef
  32. def toString (): String

    Definition Classes
    AnyRef → Any
  33. implicit def typeCheckedEqualityConstraint [A, B] (implicit equalityOfA: Equality[A], ev: <:<[B, A]): EqualityConstraint[A, B]

    Provides an EqualityConstraint[A, B] class for any two types A and B, enforcing the type constraint that B must be a subtype of A, given an implicit Equality[A].

    Provides an EqualityConstraint[A, B] class for any two types A and B, enforcing the type constraint that B must be a subtype of A, given an implicit Equality[A].

    The implicitly passed Equality[A] must be used to determine equality by the returned EqualityConstraint's areEqual method.

    This method is overridden and made implicit by subtraits TypeCheckedTripleEquals) and TypeCheckedLegacyTripleEquals, and overriden as non-implicit by the other subtraits in this package.

    equalityOfA

    an Equality[A] type class to which the EqualityConstraint.areEqual method will delegate to determine equality.

    ev

    evidence that B is a subype of A

    returns

    an EqualityConstraint[A, B] whose areEqual method delegates to the areEqual method of the passed Equality[A].

    Attributes
    implicit
    Definition Classes
    TypeCheckedTripleEqualsEqualityConstraints
  34. def unconstrainedEquality [A, B] (implicit equalityOfA: Equality[A]): EqualityConstraint[A, B]

    Provides an EqualityConstraint[A, B] class for any two types A and B, with no type constraint enforced, given an implicit Equality[A].

    Provides an EqualityConstraint[A, B] class for any two types A and B, with no type constraint enforced, given an implicit Equality[A].

    The implicitly passed Equality[A] must be used to determine equality by the returned EqualityConstraint's areEqual method.

    This method is overridden and made implicit by subtraits TripleEquals and LegacyTripleEquals, and overriden as non-implicit by the other subtraits in this package.

    equalityOfA

    an Equality[A] type class to which the EqualityConstraint.areEqual method will delegate to determine equality.

    returns

    an EqualityConstraint[A, B] whose areEqual method delegates to the areEqual method of the passed Equality[A].

    Definition Classes
    TypeCheckedTripleEqualsEqualityConstraints
  35. def wait (): Unit

    Attributes
    final
    Definition Classes
    AnyRef
    Annotations
    @throws()
  36. def wait (arg0: Long, arg1: Int): Unit

    Attributes
    final
    Definition Classes
    AnyRef
    Annotations
    @throws()
  37. def wait (arg0: Long): Unit

    Attributes
    final
    Definition Classes
    AnyRef
    Annotations
    @throws()

Inherited from LowPriorityTypeCheckedConstraint

Inherited from EqualityConstraints

Inherited from AnyRef

Inherited from Any