Kotlin mutablelist to immutable

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Immutable persistent collections for Kotlin

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Kotlin/kotlinx.collections.immutable

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`toImmutable()` -> `toImmutableList()`

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README.md

Immutable Collections Library for Kotlin

Immutable collection interfaces and implementation prototypes for Kotlin.

This is a multiplatform library providing implementations for jvm , js (both Legacy and IR), mingwX64 , linuxX64 and Apple Kotlin/Native targets.

For further details see the proposal.

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 use the functions persistentListOf , persistentSetOf , and persistentMapOf .

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 can be used.

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.toImmutableList(): ImmutableListT> fun Iterable.toImmutableSet(): ImmutableSetT>

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.toPersistentList(): PersistentListT> fun Iterable.toPersistentSet(): PersistentSetT>

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 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:

Note that the library is experimental and the API is subject to change.

The library is published to Maven Central repository.

The library depends on the Kotlin Standard Library of the version at least 1.6.0 .

Add the Maven Central repository:

Add the library to dependencies of the platform source set, e.g.:

kotlin < sourceSets < commonMain < dependencies < implementation("org.jetbrains.kotlinx:kotlinx-collections-immutable:0.3.5") > > > >

The Maven Central repository is available for dependency lookup by default. Add dependencies (you can also add other modules that you need):

dependency> groupId>org.jetbrains.kotlinxgroupId> artifactId>kotlinx-collections-immutable-jvmartifactId> version>0.3.5version> dependency>

You can build and install artifacts to maven local with:

Источник

[Solved]-How to turn a Mutable Collection into an Immutable one-kotlin

Currently in Kotlin stdlib there are no implementations of List ( Map ) that would not also implement MutableList ( MutableMap ). However due to Kotlin’s delegation feature the implementations become one liners:

class ImmutableList(private val inner:List) : List by inner class ImmutableMap(private val inner: Map) : Map by inner 

You can also enhance the creation of the immutable counterparts with extension methods:

fun Map.toImmutableMap(): Map < if (this is ImmutableMap) < return this >else < return ImmutableMap(this) >> fun List.toImmutableList(): List < if (this is ImmutableList) < return this >else < return ImmutableList(this) >> 

The above prevents a caller from modifying the List ( Map ) by casting to a different class. However there are still reasons to create a copy of the original container to prevent subtle issues like ConcurrentModificationException:

class ImmutableList private constructor(private val inner: List) : List by inner < companion object < fun create(inner: List) = if (inner is ImmutableList) < inner >else < ImmutableList(inner.toList()) >> > class ImmutableMap private constructor(private val inner: Map) : Map by inner < companion object < fun create(inner: Map) = if (inner is ImmutableMap) < inner >else < ImmutableMap(hashMapOf(*inner.toList().toTypedArray())) >> > fun Map.toImmutableMap(): Map = ImmutableMap.create(this) fun List.toImmutableList(): List = ImmutableList.create(this) 

While the above is not hard to implement there are already implementations of immutable lists and maps in both Guava and Eclipse-Collections.

If you need to convert MutableMap strictly to ImmutableMap , this will not work

val iMap : ImmutableMap = mutMap.toMap() // error 

I have found the only working way:

val iMap : ImmutableMap = ImmutableMap.builder().putAll(mutMap).build() 

Use simple bellow codes to convert Mutable Collections into an Immutable one:

val mutableList = mutableListOf() val immutableList: List = mutableList 

AlirezA Barakati 715

A classic solution is to copy your data, so that even if modified, the change would not affect the private class property:

class School < private val roster = mutableMapOf>() fun db(): Map> = roster.mapValuestTo > 

voddan 29018

I know this a Kotlin specific question and @Malt is correct but I would like to add an alternative. In particular I find Eclipse Collections, formally GS-Collections, as a better alternative to Guava for most cases and it supplements Kotlin’s built in collections well.

Simply call toMap() on your MutableMap .

val myMap = mutableMapOf("x" to "y").toMap() 

The same also works for lists.

Renann 524

As mentioned here and here, you’d need to write your own List implementation for that, or use an existing one (Guava’s ImmutableList comes to mind, or Eclipse Collections as Andrew suggested).

Kotlin enforces list (im)mutability by interface only. There are no List implementations that don’t also implement MutableList .

Even the idiomatic listOf(1,2,3) ends up calling Kotlin’s ArraysUtilJVM.asList() which calls Java’s Arrays.asList() which returns a plain old Java ArrayList .

If you care more about protecting your own internal list, than about the immutability itself, you can of course copy the entire collection and return it as an List , just like Kotlin does:

Malt 27499

Use Collections to converts a Mutable list to Immutable list, Example:

val mutableList = mutableListOf() 

Converts to Immutable list:

val immutableList = Collections.unmodifiableList(mutableList) 

Benny 1908

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