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October 15, 2019 15:01
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| package com.lenguyenthanh.functional | |
| import arrow.core.None | |
| import arrow.core.Option | |
| import arrow.core.Some | |
| import arrow.core.extensions.list.functorFilter.filterMap | |
| import arrow.core.extensions.list.functorFilter.flattenOption | |
| import arrow.core.toOption | |
| /** | |
| * A combined `map` and `filter`. Filtering is handled via `Option` | |
| * instead of `Boolean` such that the output type `B` can be different than | |
| * the input type `A`. | |
| * | |
| * Example: | |
| * {{{ | |
| * scala> import cats.implicits._ | |
| * scala> val m: Map[Int, String] = Map(1 -> "one", 3 -> "three") | |
| * scala> val l: List[Int] = List(1, 2, 3, 4) | |
| * scala> def asString(i: Int): Option[String] = m.get(i) | |
| * scala> l.mapFilter(asString) | |
| * res0: List[String] = List(one, three) | |
| * }}} | |
| */ | |
| fun filterMapExample() { | |
| val m = mapOf(1 to "one", 3 to "three") | |
| val l = listOf(1, 2, 3, 4) | |
| fun asString(i: Int): Option<String> = m[i].toOption() | |
| val filtered = l.filterMap { asString(it) } // listOf("one", "three") | |
| println(filtered) | |
| } | |
| /** | |
| * Similar to [[mapFilter]] but uses a partial function instead of a function | |
| * that returns an `Option`. | |
| * | |
| * Example: | |
| * {{{ | |
| * scala> import cats.implicits._ | |
| * scala> val l: List[Int] = List(1, 2, 3, 4) | |
| * scala> FunctorFilter[List].collect(l){ | |
| * | case 1 => "one" | |
| * | case 3 => "three" | |
| * | } | |
| * res0: List[String] = List(one, three) | |
| * }}} | |
| */ | |
| // we dont have collect now | |
| /** | |
| * "Flatten" out a structure by collapsing `Option`s. | |
| * Equivalent to using `mapFilter` with `identity`. | |
| * | |
| * Example: | |
| * {{{ | |
| * scala> import cats.implicits._ | |
| * scala> val l: List[Option[Int]] = List(Some(1), None, Some(3), None) | |
| * scala> l.flattenOption | |
| * res0: List[Int] = List(1, 3) | |
| * }}} | |
| */ | |
| fun flattenOptionExample() { | |
| val l = listOf(Some(1), None, Some(3), None) | |
| val flatten = l.flattenOption() | |
| println(flatten) | |
| } | |
| fun main() { | |
| filterMapExample() | |
| flattenOptionExample() | |
| } |
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