Double
Ordering
s for Double
s.
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
Type members
Classlikes
An ordering for Double
s which is consistent with IEEE specifications
whenever possible.
An ordering for Double
s which is consistent with IEEE specifications
whenever possible.
lt
,lteq
,equiv
,gteq
andgt
are consistent with primitive comparison operations forDouble
s, and returnfalse
when called withNaN
.min
andmax
are consistent withmath.min
andmath.max
, and returnNaN
when called withNaN
as either argument.compare
behaves the same as java.lang.Double.compare.
Because the behavior of Double
s 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
An ordering for Double
s 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 Double
s 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 Double
s 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