org.scalautils

EqualityConstraints

trait EqualityConstraints extends AnyRef

Trait that defines abstract methods used to enforce compile-time type constraints for equality comparisons, and defines === and !== operators used by matchers.

This abstract methods of this trait are selectively implemented as implicit by subclasses to enable a spectrum of type constraints for the === and !== operators. As an illustration, if in the expression, a === b, the type of a is A and b is B, the following three levels of compile-time checking can be obtained from EqualityConstraints subtraits:

Unchecked - A and B can be any two types. This (weakest) constraint level is available from subtraits TripleEquals and LegacyTripleEquals.

Conversion checked - A must be a subtype of B, or vice versa, or an implicit conversion must be available that converts A to B, or vice versa. (Both A and B can be the same type, because a type is considered a subtype of itself.) This (intermediate) constraint level is available from subtraits ConversionCheckedTripleEquals and ConversionCheckedLegacyTripleEquals.

Type checked - A must be a subtype of B, or vice versa. (Both A and B can be the same type, because a type is considered a subtype of itself.) This (strongest) constraint level is available from subtraits TypeCheckedTripleEquals and TypeCheckedLegacyTripleEquals.

The difference between the regular and “legacy” variants of each pair of traits is that the === and !== operators provided by the regular variants result in Boolean, whereas those of the legacy variants result in Option[String]. For example, were you to mix in TripleEquals, the expression 1 + 1 === 3 would return false. Were you to mix in LegacyTripleEquals, by contrast, the expression 1 + 1 === 3 would return Some("2 did not equal 3").

The purpose of the legacy variants is to maintain compatibility with existing code that uses ScalaTest's original === defined in trait org.scalatest.Assertions. This === operator returned an Option[String] to facilitate better error messages. With the advent of macros in Scala 2.10, it is possible to obtain good error messages by making assert a macro. Once ScalaTest no longer supports Scala 2.9, the legacy variants (LegacyTripleEquals, ConversionCheckedLegacyTripleEquals, and TypeCheckedLegacyTripleEquals) will be deprecated and eventually removed, === will return only Boolean, and good error messages will be obtained via macros.

This trait defines all methods that need to be defined implicitly by the six subtraits so that if multiple subtraits are used together, the inner-most subtrait in scope can not only enable the implicits it needs by overriding or hiding those methods (currently-in-scope as regular, non-implicit methods) and making them implicit, it can also disable any implicits enabled by its sibling subtraits in enclosing scopes. For example, if your test class mixes in TypeCheckedTripleEquals, inside your test class the following methods will be implicit:

If in the body of a test you want to turn off the type checking, you can import the members of TripleEquals in the body of that test. This will not only hide non-implicit methods convertToEqualizer unconstrainedEquality of TypeCheckedTripleEquals, replacing those with implicit ones defined in TripleEquals, it will also hide the three methods made implicit in TypeCheckedTripleEquals (and listed above), replacing them by non-implicit ones.

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.

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Abstract Value Members

  1. 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].

    Attributes
    abstract
  2. 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
    abstract
  3. 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.

    Attributes
    abstract
  4. 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.

    Attributes
    abstract
  5. 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.

    Attributes
    abstract
  6. 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
    abstract
  7. 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].

    Attributes
    abstract
  8. 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
    abstract
  9. 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
    abstract
  10. 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].

    Attributes
    abstract

Concrete Value Members

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

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  2. def != (arg0: Any): Boolean

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  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.

  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.

  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.

  6. def ## (): Int

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  7. def == (arg0: AnyRef): Boolean

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  8. def == (arg0: Any): Boolean

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  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.

  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.

  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.

  12. def asInstanceOf [T0] : T0

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  13. def clone (): AnyRef

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  14. def eq (arg0: AnyRef): Boolean

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  15. def equals (arg0: Any): Boolean

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    AnyRef → Any
  16. def finalize (): Unit

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  17. def getClass (): java.lang.Class[_]

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  18. def hashCode (): Int

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  19. def isInstanceOf [T0] : Boolean

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  20. def ne (arg0: AnyRef): Boolean

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  21. def notify (): Unit

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  22. def notifyAll (): Unit

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  23. def synchronized [T0] (arg0: ⇒ T0): T0

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  24. def toString (): String

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  25. def wait (): Unit

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  26. def wait (arg0: Long, arg1: Int): Unit

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  27. def wait (arg0: Long): Unit

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