Kotlin language features and proposals

JetBrains evolves the Kotlin language according to the Kotlin language evolution principles, guided by pragmatic design.

Exploration and design	Rich Errors: Error union types KEEP proposal: Not defined YouTrack issue: KT-68296
Exploration and design	Name-based destructuring KEEP proposal: Not defined YouTrack issue: KT-19627
Exploration and design	Support immutability KEEP notes: immutability YouTrack issue: KT-77734
KEEP discussion	Kotlin statics and static extensions KEEP proposal: statics.md YouTrack issue: KT-11968
KEEP discussion	Collection literals KEEP proposal: collection-literals.md YouTrack issue: KT-43871
KEEP discussion	Explicit backing fields KEEP proposal: explicit-backing-fields.md YouTrack issue: KT-14663
KEEP discussion	Version overloading KEEP proposal: version-overloading.md
KEEP discussion	Unused return value checker KEEP proposal: unused-return-value-checker.md YouTrack issue: KT-12719
KEEP discussion	Streamline KDoc ambiguity links KEEP proposal: streamline-KDoc-ambiguity-references.md GitHub issues: dokka/#3451, dokka/#3179, dokka/#3334
KEEP discussion	Resolution of links to extensions in KDoc KEEP proposal: links-to-extensions.md GitHub issue: dokka/#3555
In preview	Context parameters: support for context-dependent declarations KEEP proposal: context-parameters.md YouTrack issue: KT-14663 Available since: 2.2.0
In preview	Improvements to annotation use-site targets on properties KEEP proposal: Improvements to annotation use-site targets on properties YouTrack issue: KT-19289 Available since: 2.2.0
In preview	Nested (non-capturing) type aliases KEEP proposal: Nested (non-capturing) type aliases YouTrack issue: KT-45285 Available since: 2.2.0
In preview	Context-sensitive resolution KEEP proposal: context-sensitive-resolution.md YouTrack issue: KT-16768 Available since: 2.2.0
In preview	Expose boxed inline value classes in JVM KEEP proposal: jvm-expose-boxed.md YouTrack issue: KT-28135 Available since: 2.2.0
In preview	kotlin.time.Instant KEEP proposal: Instant and Clock Available since: 2.1.0
In preview	Uuid KEEP proposal: uuid.md YouTrack issue: KT-31880 Available since: 2.0.20
In preview	Common Atomics and Atomic Arrays KEEP proposal: Common atomics YouTrack issue: KT-62423 Available since: 2.2.0
In preview	KMP Kotlin-to-Java direct actualization KEEP proposal: kmp-kotlin-to-java-direct-actualization.md YouTrack issue: KT-67202 Available since: 2.1.0
Stable	Guard conditions in when-with-subject KEEP proposal: guards.md YouTrack issue: KT-13626 Available since: 2.2.0
Stable	Multidollar interpolation: improved handling of `$` in string literals KEEP proposal: dollar-escape.md YouTrack issue: KT-2425 Available since: 2.2.0
Stable	Non-local `break` and `continue` KEEP proposal: break-continue-in-inline-lambdas.md YouTrack issue: KT-1436 Available since: 2.2.0
Stable	Stabilized `@SubclassOptInRequired` KEEP proposal: subclass-opt-in-required.md YouTrack issue: KT-54617 Available since: 2.1.0
Stable	`Enum.entries`: performant replacement of the `Enum.values()` KEEP proposal: enum-entries.md YouTrack issue: KT-48872 Target version: 2.0.0
Stable	Data objects KEEP proposal: data-objects.md YouTrack issue: KT-4107 Target version: 1.9.0
Stable	RangeUntil operator `..<` KEEP proposal: open-ended-ranges.md YouTrack issue: KT-15613 Target version: 1.7.20
Stable	Definitely non-nullable types KEEP proposal: definitely-non-nullable-types.md YouTrack issue: KT-26245 Target version: 1.7.0
Revoked	Context receivers KEEP proposal: context-receivers.md YouTrack issue: KT-10468 Replaced with context-parameters.md
Revoked	Java synthetic property references KEEP proposal: references-to-java-synthetic-properties.md YouTrack issue: KT-8575

Exploration and design

Rich Errors: Error union types

KEEP proposal: Not defined
YouTrack issue: KT-68296

Exploration and design

Name-based destructuring

KEEP proposal: Not defined
YouTrack issue: KT-19627

Exploration and design

Support immutability

KEEP notes: immutability
YouTrack issue: KT-77734

KEEP discussion	Kotlin statics and static extensions KEEP proposal: statics.md YouTrack issue: KT-11968
KEEP discussion	Collection literals KEEP proposal: collection-literals.md YouTrack issue: KT-43871
KEEP discussion	Explicit backing fields KEEP proposal: explicit-backing-fields.md YouTrack issue: KT-14663
KEEP discussion	Version overloading KEEP proposal: version-overloading.md
KEEP discussion	Unused return value checker KEEP proposal: unused-return-value-checker.md YouTrack issue: KT-12719
KEEP discussion	Streamline KDoc ambiguity links KEEP proposal: streamline-KDoc-ambiguity-references.md GitHub issues: dokka/#3451, dokka/#3179, dokka/#3334
KEEP discussion	Resolution of links to extensions in KDoc KEEP proposal: links-to-extensions.md GitHub issue: dokka/#3555

In preview	Context parameters: support for context-dependent declarations KEEP proposal: context-parameters.md YouTrack issue: KT-14663 Available since: 2.2.0
In preview	Improvements to annotation use-site targets on properties KEEP proposal: Improvements to annotation use-site targets on properties YouTrack issue: KT-19289 Available since: 2.2.0
In preview	Nested (non-capturing) type aliases KEEP proposal: Nested (non-capturing) type aliases YouTrack issue: KT-45285 Available since: 2.2.0
In preview	Context-sensitive resolution KEEP proposal: context-sensitive-resolution.md YouTrack issue: KT-16768 Available since: 2.2.0
In preview	Expose boxed inline value classes in JVM KEEP proposal: jvm-expose-boxed.md YouTrack issue: KT-28135 Available since: 2.2.0
In preview	kotlin.time.Instant KEEP proposal: Instant and Clock Available since: 2.1.0
In preview	Uuid KEEP proposal: uuid.md YouTrack issue: KT-31880 Available since: 2.0.20
In preview	Common Atomics and Atomic Arrays KEEP proposal: Common atomics YouTrack issue: KT-62423 Available since: 2.2.0
In preview	KMP Kotlin-to-Java direct actualization KEEP proposal: kmp-kotlin-to-java-direct-actualization.md YouTrack issue: KT-67202 Available since: 2.1.0

Stable	Guard conditions in when-with-subject KEEP proposal: guards.md YouTrack issue: KT-13626 Available since: 2.2.0
Stable	Multidollar interpolation: improved handling of `$` in string literals KEEP proposal: dollar-escape.md YouTrack issue: KT-2425 Available since: 2.2.0
Stable	Non-local `break` and `continue` KEEP proposal: break-continue-in-inline-lambdas.md YouTrack issue: KT-1436 Available since: 2.2.0
Stable	Stabilized `@SubclassOptInRequired` KEEP proposal: subclass-opt-in-required.md YouTrack issue: KT-54617 Available since: 2.1.0
Stable	`Enum.entries`: performant replacement of the `Enum.values()` KEEP proposal: enum-entries.md YouTrack issue: KT-48872 Target version: 2.0.0
Stable	Data objects KEEP proposal: data-objects.md YouTrack issue: KT-4107 Target version: 1.9.0
Stable	RangeUntil operator `..<` KEEP proposal: open-ended-ranges.md YouTrack issue: KT-15613 Target version: 1.7.20
Stable	Definitely non-nullable types KEEP proposal: definitely-non-nullable-types.md YouTrack issue: KT-26245 Target version: 1.7.0

Revoked	Context receivers KEEP proposal: context-receivers.md YouTrack issue: KT-10468 Replaced with context-parameters.md
Revoked	Java synthetic property references KEEP proposal: references-to-java-synthetic-properties.md YouTrack issue: KT-8575

Revoked

Context receivers

KEEP proposal: context-receivers.md
YouTrack issue: KT-10468
Replaced with context-parameters.md

Revoked

Java synthetic property references

KEEP proposal: references-to-java-synthetic-properties.md
YouTrack issue: KT-8575

Last modified: 23 June 2025