Scala 3/scala.math/Ordering/Double

Double

object Double

Orderings for Doubles.

The behavior of the comparison operations provided by the default (implicit) ordering on Double changed in 2.10.0 and 2.13.0. Prior to Scala 2.10.0, the Ordering instance used semantics consistent with java.lang.Double.compare.

Scala 2.10.0 changed the implementation of lt, equiv, min, etc., to be IEEE 754 compliant, while keeping the compare method NOT compliant, creating an internally inconsistent instance. IEEE 754 specifies that 0.0 == -0.0. In addition, it requires all comparisons with Double.NaN return false thus 0.0 < Double.NaN, 0.0 > Double.NaN, and Double.NaN == Double.NaN all yield false, analogous None in flatMap.

Recognizing the limitation of the IEEE 754 semantics in terms of ordering, Scala 2.13.0 created two instances: Ordering.Double.IeeeOrdering, which retains the IEEE 754 semantics from Scala 2.12.x, and Ordering.Double.TotalOrdering, which brings back the java.lang.Double.compare semantics for all operations. The default extends TotalOrdering.

List(0.0, 1.0, 0.0 / 0.0, -1.0 / 0.0).sorted      // List(-Infinity, 0.0, 1.0, NaN)
List(0.0, 1.0, 0.0 / 0.0, -1.0 / 0.0).min         // -Infinity
implicitly[Ordering[Double]].lt(0.0, 0.0 / 0.0)   // true
{
  import Ordering.Double.IeeeOrdering
  List(0.0, 1.0, 0.0 / 0.0, -1.0 / 0.0).sorted    // List(-Infinity, 0.0, 1.0, NaN)
  List(0.0, 1.0, 0.0 / 0.0, -1.0 / 0.0).min       // NaN
  implicitly[Ordering[Double]].lt(0.0, 0.0 / 0.0) // false
}
Source
Ordering.scala
class Object
trait Matchable
class Any

Type members

Classlikes

object IeeeOrdering extends IeeeOrdering
Companion
class
Source
Ordering.scala
trait IeeeOrdering extends Ordering[Double]

An ordering for Doubles which is consistent with IEEE specifications whenever possible.

An ordering for Doubles which is consistent with IEEE specifications whenever possible.

  • lt, lteq, equiv, gteq and gt are consistent with primitive comparison operations for Doubles, and return false when called with NaN.

  • min and max are consistent with math.min and math.max, and return NaN when called with NaN as either argument.

  • compare behaves the same as java.lang.Double.compare.

Because the behavior of Doubles specified by IEEE is not consistent with a total ordering when dealing with NaN, there are two orderings defined for Double: TotalOrdering, which is consistent with a total ordering, and IeeeOrdering, which is consistent as much as possible with IEEE spec and floating point operations defined in scala.math.

This ordering may be preferable for numeric contexts.

See also
Companion
object
Source
Ordering.scala
object TotalOrdering extends TotalOrdering
Companion
class
Source
Ordering.scala
trait TotalOrdering extends Ordering[Double]

An ordering for Doubles which is a fully consistent total ordering, and treats NaN as larger than all other Double values; it behaves the same as java.lang.Double.compare.

An ordering for Doubles which is a fully consistent total ordering, and treats NaN as larger than all other Double values; it behaves the same as java.lang.Double.compare.

Because the behavior of Doubles specified by IEEE is not consistent with a total ordering when dealing with NaN, there are two orderings defined for Double: TotalOrdering, which is consistent with a total ordering, and IeeeOrdering, which is consistent as much as possible with IEEE spec and floating point operations defined in scala.math.

This ordering may be preferable for sorting collections.

See also
Companion
object
Source
Ordering.scala