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Diffstat (limited to 'test/files/run/t3326.scala')
-rw-r--r-- | test/files/run/t3326.scala | 74 |
1 files changed, 74 insertions, 0 deletions
diff --git a/test/files/run/t3326.scala b/test/files/run/t3326.scala new file mode 100644 index 0000000000..f70cb01504 --- /dev/null +++ b/test/files/run/t3326.scala @@ -0,0 +1,74 @@ + + + +import scala.math.Ordering + + + +/** The heart of the problem - we want to retain the ordering when + * using `++` on sorted maps. + * + * There are 2 `++` overloads - a generic one in traversables and + * a map-specific one in `MapLike` - which knows about the ordering. + * + * The problem here is that the expected return type for the expression + * in which `++` appears drives the decision of the overload that needs + * to be taken. + * The `collection.SortedMap` does not have `++` overridden to return + * `SortedMap`, but `immutable.Map` instead. + * This is why `collection.SortedMap` used to resort to the generic + * `TraversableLike.++` which knows nothing about the ordering. + * + * To avoid `collection.SortedMap`s resort to the more generic `TraverableLike.++`, + * we override the `MapLike.++` overload in `collection.SortedMap` to return + * the proper type `SortedMap`. + */ +object Test { + + def main(args: Array[String]) { + testCollectionSorted() + testImmutableSorted() + } + + def testCollectionSorted() { + import collection._ + val order = implicitly[Ordering[Int]].reverse + var m1: SortedMap[Int, String] = SortedMap.empty[Int, String](order) + var m2: SortedMap[Int, String] = SortedMap.empty[Int, String](order) + + m1 += (1 -> "World") + m1 += (2 -> "Hello") + + m2 += (4 -> "Bar") + m2 += (5 -> "Foo") + + val m3: SortedMap[Int, String] = m1 ++ m2 + + println(m1) + println(m2) + println(m3) + + println(m1 + (3 -> "?")) + } + + def testImmutableSorted() { + import collection.immutable._ + val order = implicitly[Ordering[Int]].reverse + var m1: SortedMap[Int, String] = SortedMap.empty[Int, String](order) + var m2: SortedMap[Int, String] = SortedMap.empty[Int, String](order) + + m1 += (1 -> "World") + m1 += (2 -> "Hello") + + m2 += (4 -> "Bar") + m2 += (5 -> "Foo") + + val m3: SortedMap[Int, String] = m1 ++ m2 + + println(m1) + println(m2) + println(m3) + + println(m1 + (3 -> "?")) + } +} |