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c

scala

ValueOf

final class ValueOf[T] extends AnyVal

ValueOf[T] provides the unique value of the type T where T is a type which has a single inhabitant. Eligible types are singleton types of the form stablePath.type, Unit and singleton types corresponding to value literals.

Instances of ValueOf[T] are provided implicitly for all eligible types. Typically an instance would be required where a runtime value corresponding to a type level computation is needed.

For example, we might define a type Residue[M <: Int] corresponding to the group of integers modulo M. We could then mandate that residues can be summed only when they are parameterized by the same modulus,

case class Residue[M <: Int](n: Int) extends AnyVal {
  def +(rhs: Residue[M])(implicit m: ValueOf[M]): Residue[M] =
    Residue((this.n + rhs.n) % valueOf[M])
}

val fiveModTen = Residue[10](5)
val nineModTen = Residue[10](9)

fiveModTen + nineModTen    // OK == Residue[10](4)

val fourModEleven = Residue[11](4)

fiveModTen + fourModEleven // compiler error: type mismatch;
                           //   found   : Residue[11]
                           //   required: Residue[10]

Notice that here the modulus is encoded in the type of the values and so does not incur any additional per-value storage cost. When a runtime value of the modulus is required in the implementation of + it is provided at the call site via the implicit argument m of type ValueOf[M].

Annotations
@implicitNotFound(msg = "No singleton value available for ${T}.")
Source
ValueOf.scala
Linear Supertypes
Type Hierarchy
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Inherited
  1. ValueOf
  2. AnyVal
  3. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Visibility
  1. Public
  2. Protected

Instance Constructors

  1. new ValueOf(value: T)

Value Members

  1. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

    true if !(this == that), false otherwise.

    Definition Classes
    Any
  2. final def ##: Int

    Equivalent to x.hashCode except for boxed numeric types and null.

    Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.

    returns

    a hash value consistent with ==

    Definition Classes
    Any
  3. def +(other: String): String
    Implicit
    This member is added by an implicit conversion from ValueOf[T] toany2stringadd[ValueOf[T]] performed by method any2stringadd in scala.Predef.
    Definition Classes
    any2stringadd
  4. def ->[B](y: B): (ValueOf[T], B)
    Implicit
    This member is added by an implicit conversion from ValueOf[T] toArrowAssoc[ValueOf[T]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  5. final def ==(arg0: Any): Boolean

    Test two objects for equality.

    Test two objects for equality. The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    Definition Classes
    Any
  6. final def asInstanceOf[T0]: T0

    Cast the receiver object to be of type T0.

    Cast the receiver object to be of type T0.

    Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

    returns

    the receiver object.

    Definition Classes
    Any
    Exceptions thrown

    ClassCastException if the receiver object is not an instance of the erasure of type T0.

  7. def ensuring(cond: (ValueOf[T]) => Boolean, msg: => Any): ValueOf[T]
    Implicit
    This member is added by an implicit conversion from ValueOf[T] toEnsuring[ValueOf[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  8. def ensuring(cond: (ValueOf[T]) => Boolean): ValueOf[T]
    Implicit
    This member is added by an implicit conversion from ValueOf[T] toEnsuring[ValueOf[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  9. def ensuring(cond: Boolean, msg: => Any): ValueOf[T]
    Implicit
    This member is added by an implicit conversion from ValueOf[T] toEnsuring[ValueOf[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  10. def ensuring(cond: Boolean): ValueOf[T]
    Implicit
    This member is added by an implicit conversion from ValueOf[T] toEnsuring[ValueOf[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  11. def formatted(fmtstr: String): String

    Returns string formatted according to given format string.

    Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

    Implicit
    This member is added by an implicit conversion from ValueOf[T] toStringFormat[ValueOf[T]] performed by method StringFormat in scala.Predef.
    Definition Classes
    StringFormat
    Annotations
    @inline()
  12. def getClass(): Class[_ <: AnyVal]

    Returns the runtime class representation of the object.

    Returns the runtime class representation of the object.

    returns

    a class object corresponding to the runtime type of the receiver.

    Definition Classes
    AnyValAny
  13. final def isInstanceOf[T0]: Boolean

    Test whether the dynamic type of the receiver object is T0.

    Test whether the dynamic type of the receiver object is T0.

    Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

    returns

    true if the receiver object is an instance of erasure of type T0; false otherwise.

    Definition Classes
    Any
  14. def toString(): String

    Returns a string representation of the object.

    Returns a string representation of the object.

    The default representation is platform dependent.

    returns

    a string representation of the object.

    Definition Classes
    Any
  15. val value: T

Deprecated Value Members

  1. def [B](y: B): (ValueOf[T], B)
    Implicit
    This member is added by an implicit conversion from ValueOf[T] toArrowAssoc[ValueOf[T]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @deprecated
    Deprecated

    (Since version 2.13.0) Use -> instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.

Inherited from AnyVal

Inherited from Any

Inherited by implicit conversion any2stringadd fromValueOf[T] to any2stringadd[ValueOf[T]]

Inherited by implicit conversion StringFormat fromValueOf[T] to StringFormat[ValueOf[T]]

Inherited by implicit conversion Ensuring fromValueOf[T] to Ensuring[ValueOf[T]]

Inherited by implicit conversion ArrowAssoc fromValueOf[T] to ArrowAssoc[ValueOf[T]]

Ungrouped