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Add count as syntax to UnorderedFoldable #2520
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LukaJCB
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leusgalvan:count-unordered-foldable
Sep 25, 2018
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,33 @@ | ||
package cats | ||
package syntax | ||
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import cats.instances.long._ | ||
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trait UnorderedFoldableSyntax extends UnorderedFoldable.ToUnorderedFoldableOps { | ||
implicit final def catsSyntaxUnorderedFoldableOps[F[_]: UnorderedFoldable, A](fa: F[A]): UnorderedFoldableOps[F, A] = | ||
new UnorderedFoldableOps[F, A](fa) | ||
} | ||
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final class UnorderedFoldableOps[F[_], A](val fa: F[A]) extends AnyVal { | ||
/** | ||
* Count the number of elements in the structure that satisfy the given predicate. | ||
* | ||
* For example: | ||
* {{{ | ||
* scala> import cats.implicits._ | ||
* scala> val set1 = Set[String]() | ||
* scala> set1.count_(_.length > 0) | ||
* res0: Long = 0 | ||
* | ||
* scala> val set2 = Set("hello", "world", "!") | ||
* scala> set2.count_(_.length > 1) | ||
* res1: Long = 2 | ||
* | ||
* scala> val set3 = Set(41, 32, 23) | ||
* scala> set3.count_(_ % 2 == 0) | ||
* res2: Long = 1 | ||
* }}} | ||
*/ | ||
def count_(p: A => Boolean)(implicit F: UnorderedFoldable[F]): Long = | ||
F.unorderedFoldMap(fa)(a => if (p(a)) 1L else 0L) | ||
} |
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26 changes: 26 additions & 0 deletions
26
tests/src/test/scala/cats/tests/UnorderedFoldableSuite.scala
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,26 @@ | ||
package cats | ||
package tests | ||
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import org.scalatest.prop.PropertyChecks | ||
import org.scalacheck.Arbitrary | ||
import cats.instances.all._ | ||
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abstract class UnorderedFoldableSuite[F[_]: UnorderedFoldable](name: String)( | ||
implicit ArbFString: Arbitrary[F[String]]) extends CatsSuite with PropertyChecks { | ||
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def iterator[T](fa: F[T]): Iterator[T] | ||
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test(s"UnorderedFoldable[$name].count") { | ||
forAll { (fa: F[String], p: String => Boolean) => | ||
fa.count_(p) === iterator(fa).count(p).toLong | ||
} | ||
} | ||
} | ||
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class UnorderedFoldableSetSuite extends UnorderedFoldableSuite[Set]("set") { | ||
def iterator[T](set: Set[T]): Iterator[T] = set.iterator | ||
} | ||
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class UnorderedFoldableMapSuite extends UnorderedFoldableSuite[Map[String, ?]]("map") { | ||
def iterator[T](map: Map[String, T]): Iterator[T] = map.valuesIterator | ||
} |
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Maybe it'd be better to have
count
defined in theUnorderedFoldable
trait itself, and only callcount
here? Otherwise you can only use it with the syntax implicits, and not justF.count
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You can't do that if you want to maintain binary compat.
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Aww damn :( the encoding of traits strikes again
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we should be able to define extensions for typeclass instances, like: