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Overview
Kotlin for Server Side
Kotlin for Android
Kotlin for JavaScript
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Kotlin for Data Science
Coroutines
Multiplatform
What's New
What's New in 1.4
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
Functional (SAM) Interfaces
Visibility Modifiers
Extensions
Data Classes
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Generics
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Objects
Type Aliases
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Delegation
Delegated Properties
Functions and Lambdas
Functions
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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
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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
Kotlin Multiplatform
Create a multiplatform library
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Publish a multiplatform library
Build final native binaries
Supported platforms
Multiplatform Gradle DSL Reference
Migrating to Kotlin 1.4
More Language Constructs
Destructuring Declarations
Type Checks and Casts
This expressions
Equality
Operator overloading
Null Safety
Exceptions
Annotations
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Scope Functions
Type-Safe Builders
Opt-in Requirements
Core Libraries
Standard Library
kotlin.test
Reference
Keywords and operators
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Coding style conventions
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
IR Compiler
Generating External Declarations with Dukat
Native
Concurrency
Immutability
Kotlin Libraries
Platform Libraries
C Interop
Objective-C and Swift Interop
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Debugging
FAQ
Tools
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Evolution
Kotlin Evolution
Stability of Kotlin components
Compatibility Guide for Kotlin 1.3
Compatibility Guide for Kotlin 1.4
FAQ
FAQ
Comparison to Java
kotlin-stdlib / kotlin.collections / HashMap / keys

keys

Common
Native
1.0
val keys: MutableSet<K>

Returns a MutableSet of all keys in this map.

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Kotlin™ is protected under the Kotlin Foundation and licensed under the Apache 2 license. Supported and developed by JetBrains
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