Immutable Collections Library for Kotlin
Immutable collection interfaces and implementation prototypes for Kotlin.
For further details see the proposal.
What's in this library
Interfaces and implementations
This library provides interfaces for immutable and persistent collections.
Immutable collection interfaces
Interface | Bases |
---|---|
ImmutableCollection |
Collection |
ImmutableList |
ImmutableCollection , List |
ImmutableSet |
ImmutableCollection , Set |
ImmutableMap |
Map |
Persistent collection interfaces
Interface | Bases |
---|---|
PersistentCollection |
ImmutableCollection |
PersistentList |
PersistentCollection , ImmutableList |
PersistentSet |
PersistentCollection , ImmutableSet |
PersistentMap |
ImmutableMap |
Persistent collection builder interfaces
Interface | Bases |
---|---|
PersistentCollection.Builder |
MutableCollection |
PersistentList.Builder |
PersistentCollection.Builder , MutableList |
PersistentSet.Builder |
PersistentCollection.Builder , MutableSet |
PersistentMap.Builder |
MutableMap |
To instantiate an empty persistent collection or a collection with the specified elements the functions
persistentListOf
, persistentSetOf
, and persistentMapOf
can be used.
The default implementations of PersistentSet
and PersistentMap
, which are returned by persistentSetOf
and persistentMapOf
,
preserve the element insertion order during iteration. This comes at expense of maintaining more complex data structures.
If the order of elements doesn't matter, the more efficient implementations returned by the functions
persistentHashSetOf
and persistentHashMapOf
could be used.
Operations
toImmutableList/Set/Map
Converts a read-only or mutable collection to an immutable one. If the receiver is already immutable and has the required type, returns it as is.
fun Iterable<T>.toImmutableList(): ImmutableList<T>
fun Iterable<T>.toImmutableSet(): ImmutableSet<T>
toPersistentList/Set/Map
Converts a read-only or mutable collection to a persistent one.
If the receiver is already persistent and has the required type, returns it as is.
If the receiver is a builder of the required persistent collection type, calls build
on it and returns the result.
fun Iterable<T>.toPersistentList(): PersistentList<T>
fun Iterable<T>.toPersistentSet(): PersistentSet<T>
+
and -
operators
plus
and minus
operators on persistent collections exploit their immutability
and delegate the implementation to the collections themselves.
The operation is performed with persistence in mind: the returned immutable collection may share storage
with the original collection.
val newList = persistentListOf("a", "b") + "c"
// newList is also a PersistentList
Note: you need to import these operators from
kotlinx.collections.immutable
package in order for them to take the precedence over the ones from the standard library.
import kotlinx.collections.immutable.*
Mutate
mutate
extension function simplifies quite common pattern of persistent collection modification:
get a builder, apply some mutating operations on it, transform it back to a persistent collection:
collection.builder().apply { some_actions_on(this) }.build()
With mutate
it transforms to:
collection.mutate { some_actions_on(it) }
Using in your projects
Note that the library is experimental and the API is subject to change.
The library is published to kotlinx bintray repository.
The library depends on the Kotlin Standard Library of the version at least 1.3.30
.
Maven
Add the bintray repository to <repositories>
section:
<repository>
<snapshots>
<enabled>false</enabled>
</snapshots>
<id>kotlinx</id>
<name>bintray</name>
<url>https://dl.bintray.com/kotlin/kotlinx</url>
</repository>
Add dependencies (you can also add other modules that you need):
<dependency>
<groupId>org.jetbrains.kotlinx</groupId>
<artifactId>kotlinx-collections-immutable</artifactId>
<version>0.2</version>
</dependency>
Gradle
Add the bintray repository:
repositories {
maven {
url "https://dl.bintray.com/kotlin/kotlinx"
}
}
Add the dependency:
compile 'org.jetbrains.kotlinx:kotlinx-collections-immutable:0.2'
Building from source
You can build and install artifacts to maven local with:
gradlew build install