Kotlin 1.3.70
Learn Community Play
Overview
Kotlin for Server Side
Kotlin for Android
Kotlin for JavaScript
Kotlin for Native
Kotlin for Data Science
Coroutines
Multiplatform
What's New
What's New in 1.3
What's New in 1.2
What's New in 1.1
Getting Started
Basic Syntax
Idioms
Coding Conventions
Basics
Basic Types
Packages and Imports
Control Flow
Returns and Jumps
Classes and Objects
Classes and Inheritance
Properties and Fields
Interfaces
Visibility Modifiers
Extensions
Data Classes
Sealed Classes
Generics
Nested Classes
Enum Classes
Objects
Type Aliases
Inline Classes
Delegation
Delegated Properties
Functions and Lambdas
Functions
Lambdas
Inline Functions
Collections
Collections Overview
Constructing Collections
Iterators
Ranges and Progressions
Sequences
Operations Overview
Transformations
Filtering
Plus and Minus Operators
Grouping
Retrieving Collection Parts
Retrieving Single Elements
Ordering
Aggregate Operations
Collection Write Operations
List Specific Operations
Set Specific Operations
Map Specific Operations
Coroutines
Coroutines Guide
Basics
Cancellation and Timeouts
Composing Suspending Functions
Coroutine Context and Dispatchers
Asynchronous Flow
Channels
Exception Handling and Supervision
Shared Mutable State and Concurrency
Select Expression (experimental)
Multiplatform Programming
Platform-Specific Declarations
Building with Gradle
More Language Constructs
Destructuring Declarations
Type Checks and Casts
This expressions
Equality
Operator overloading
Null Safety
Exceptions
Annotations
Reflection
Scope Functions
Type-Safe Builders
Opt-in Requirements
Core Libraries
Standard Library
kotlin.test
Reference
Keywords and Operators
Grammar
Java Interop
Calling Java from Kotlin
Calling Kotlin from Java
JavaScript
Setting Up a Project
Dynamic Type
Calling JavaScript from Kotlin
Calling Kotlin from JavaScript
JavaScript Modules
JavaScript Reflection
JavaScript DCE
Native
Concurrency
Immutability
Kotlin Libraries
Platform Libraries
C Interop
Objective-C and Swift Interop
Symbolicating iOS crash reports
CocoaPods Integration
Gradle Plugin
Debugging
FAQ
Tools
Documenting Kotlin Code
Using Kapt
Kotlin Compiler Options
Using Gradle
Using Maven
Using Ant
Kotlin and OSGi
Compiler plugins
Coding Conventions
Evolution
Kotlin Evolution
Stability of different components
Compatibility Guide for Kotlin 1.3
FAQ
FAQ
Comparison to Java
kotlin-stdlib / kotlin.collections / MutableMap / keys

keys

Common
JVM
JS
Native
1.0
abstract val keys: MutableSet<K>

Returns a MutableSet of all keys in this map.

  • Blog
  • Forum
  • Bug tracker
  • Github
  • Twitter

Contributing to Kotlin

Press kit

Licensed under the Apache 2 license
Kotlin Trademark is protected under the Kotlin Foundation
Sponsored and developed by JetBrains
esc