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KotlinConf 2025 Recordings

My list of must-watch from KotlinConf 2025.

Coroutines Races Guessing Game!

A fun game that pushes your understanding of Kotlin Coroutines.

KotlinConf 2025 Announcements

The greatest announcements from KotlinConf 2025.

Coroutines Mastery

5-weeks-long kohort workshop to master Kotlin Coroutines.

Benefit: Open Workshop Recording

Introduction of the new benefit for open workshops attendees.

Kotlin Compiler Plugins

All you need to know about Kotlin Compiler plugins.

The problems of Kotlin/Wasm I had when making a game

A short story of the problems I needed to face when publishing a simple game made with Kotlin/Wasm.

Collection Processing Guessing Game!

A fun game that pushes your understanding of Kotlin collection processing.

How modifiers order affects Compose UI appearance

A complete explanation of how modifier order affects the appearance of your Jetpack Compose UI.

Kotlin Christmas Dream

My dream about the future of Kotlin.

Marcin Moskała
Marcin Moskała12/24/2024

Is reflection slowing down your code?

Let's benchmark reflection and see how it affects the performance of your code.

Marcin Moskała
Marcin Moskała12/16/2024

Jetpack Compose Modifier Guessing Game!

A fun game to learn about Jetpack Compose modifiers.

Using BlockHound to track blocking calls in non-blocking dispatchers

How to use BlockHound to track blocking calls in non-blocking dispatchers.

Representing ViewModel events with StateFlow vs. SharedFlow vs. Channel

What is the best way to represent ViewModel events in Kotlin?

Marcin Moskała
Marcin Moskała11/18/2024

The best dispatcher for a backend framework

Let's explore different dispatchers and find the best one for a backend request handlers.

Marcin Moskała
Marcin Moskała11/13/2024

Win a Free Ticket to Droidcon Italy!

Upgrade your Kotlin skills and win a free ticket to Droidcon Italy!

Halina Ciccone
Halina Ciccone10/21/2024

Books for 2025 company workshops attendees promotion

Our special promotion for company workshops organised in 2025.

Marcin Moskała
Marcin Moskała10/19/2024

Why using Kotlin Coroutines?

The explanation of why coroutines stand out and offer us what hasn't been offered by other technologies.

Which Kotlin workshop to choose?

A short guide how to choose the best workshop for you.

Item 31: Respect abstraction contracts

Just because we can do something, does not mean we should. How to respect abstraction contracts and why it is so important.

Job and children awaiting in Kotlin Coroutines

What Job is and how it is the most important context responsible for structured concurrency.

Finance your workshop by company

How to get your workshop financed by your company.

Item 30: Define contracts with documentation

How do we express our library or module contracts and why are they so important.

Kotlin Coroutines dispatchers

Where we should use each dispatcher from the Kotlin Coroutines library.

SharedFlow vs StateFlow

When to use SharedFlow and when to use StateFlow.

Item 27: Specify API stability

How do we specify API stability and why it is so important.

Power Assert now in Kotlin!

What is Power Assert, how to use it, and how it works in Kotlin.

The problem of union types for type systems

Why union types are not such a good idea for static type systems.

Key advantages of Kotlin Coroutines

Where Kotlin Coroutines shine and why you should use them.

Cancellation in Kotlin Coroutines

Everything you need to know about the cancellation mechanism in Kotlin Coroutines.

Mutable objects or properties?

Time to answer the question: var/readonly vs val/mutable. Which one should you use?

Learn Kotlin with Marcin Moskała

See what materials and options from Marcin Moskala you can have to learn Kotlin.

The third edition of Kotlin Coroutines: Deep Dive book is finally ready!

Learn about the new release of the famous book about Kotlin Coroutines.

Updates in Kotlin for Developers series

Noticed any changes in our Kotlin for Developers series? Here's what's new!

How many threads does your network client use?

Many popular network clients consume way more threads than you might expect. Let's overview the problem and find a solution.

Kotlin bites on X/Twitter 3

A collection of Kotlin bites of knowledge, in a form of tweets.

Item 29: Minimize elements’ visibility

Why we should minimize elements’ visibility and how to do it.

Item 28: Consider wrapping external APIs

Why we should wrap external APIs and how to do it.

A Pattern for Composing Flow Operations

Extending and operating on top of your existing flows

Renato Costa
Renato Costa4/15/2024

Why Non-Blocking?

From blocking to non-blocking with Kotlin, Coroutines and Spring Boot

Renato Costa
Renato Costa3/25/2024

Books for 2024 company workshops attendees promotion

Our special promotion for company workshops organised in 2024.

Generics in Kotlin

The essence of how generics work in Kotlin.

flatMapMerge is... weird

How not to get surprised by flatMapMerge behavior.

KotlinConf 2024 - what is this all about?

Exploring the Biggest Kotlin Conference

What is CoroutineContext and how does it work?

A deep explanation of the coroutine context - the powerful data holder for coroutines.

Item 26: Use abstraction to protect code against changes

How do we abstract elements, and what are the consequences.

Item 25: Each function should be written in terms of a single level of abstraction

Why each function should be written in terms of a single level of abstraction and how to achieve it.

Abstraction design: Introduction

What is abstraction in programming and why is it so important.

Effective Kotlin Item 20: Do not repeat common algorithms

Why extracting utility functions is so important for our programs.

Static Code Analysers

All you need to know about Static Code Analysers and Detekt.

Nicola
Nicola1/22/2024

Functional Kotlin now with exercises

Functional Kotlin was updated! Now it has exercises to help readers practice the knowledge.

Effective Kotlin Item 19: Do not repeat knowledge

Why knowledge repetition is so problematic and how it relates to the single responsibility principle.

Simulating dice casting, to calculate Risc game fairness

Using programming to simulate a battle in Risc, and learn about its fairness.

Big Kotlin Challenge

Do you want to learn Kotlin? Join our Big Kotlin Challenge!

Marcin Moskała
Marcin Moskała12/28/2023

JavaScript interoperability

How to interoperate between Kotlin and JavaScript.

Marcin Moskała
Marcin Moskała12/18/2023

Annotation Processing

Implement your first annotation processor in Kotlin.

Marcin Moskała
Marcin Moskała12/11/2023

Effective Kotlin Item 60: Use appropriate collection types

Using non-standard collection types to improve performance in Kotlin.

Kotlin Symbol Processing

All the essential aspects of KSP in practice.

Marcin Moskała
Marcin Moskała11/27/2023

Effective Kotlin Item 49: Use caching when possible

Why we should use caching and how to do it.

Marcin Moskała
Marcin Moskała11/20/2023

Kotlin Essentials now with exercises

Kotlin Essentials was updated! Now it has exercises to help readers practice the knowledge.

Marcin Moskała
Marcin Moskała11/14/2023

Data classes in Kotlin

What are data classes in Kotlin and how do we use them.

Marcin Moskała
Marcin Moskała11/13/2023

Get an ebook if you have a paperback!

Special promotion until the end of this year, we give away ebooks for paperback owners who post their photos with those books.

Effective Kotlin Item 48: Consider using object declarations

Why we should use object declarations instead of regular classes.

Kotlin Reflection: Type references

Using type references, with practical example of random value generator.

Marcin Moskała
Marcin Moskała10/30/2023

Kotlin Reflection: Class references

All the essential aspects of class references, and a practical object serialization example.

Marcin Moskała
Marcin Moskała10/23/2023

Kotlin books for conferences and universities

We have a very special offers for conferences and universities that want to give away books.

Marcin Moskała
Marcin Moskała10/17/2023

Kotlin Reflection: Method and property references

The general hierarchy of Kotlin reference classes, and details about method and property references.

Marcin Moskała
Marcin Moskała10/16/2023

Kotlin for developers' series is finally ready!

We are happy to announce that Kotlin for developers series is finally complete.

Marcin Moskała
Marcin Moskała10/12/2023

Extensions in Kotlin

What are extensions in Kotlin and how do we use them.

Effective Kotlin Item 35: Consider using dependency injection

What is dependency injection, why it is so important, and how to use it in Kotlin.

Kotlin for Developers series is updated to Kotlin 1.9 and ready for 2.0

All the books from the series Kotlin for Developers are ready for Kotlin 2.0!

Implementing Multiplatform Kotlin Mobile

How in Kotlin we can implement Android and iOS projects with shared logic.

Implementing Multiplatform Kotlin library

How in Kotlin we can use multiplatform capabilities to distribute the same code to multiple platforms.

Using Multiplatform Kotlin

The essence of using multiplatform Kotlin capabilities and definition common elements.

The story behind the lighthouse

The story behind the lighthouse used on the new edition of Effective Kotlin.

The second edition of Effective Kotlin: Best Practices is finally ready!

Learn about the new release of the famous book about the best practices for Kotlin development.

Sealed classes and interfaces in Kotlin

What are sealed classes and interfaces in Kotlin and how do we use them.

Effective Kotlin Item 2: Eliminate critical sections

Learn why do we need to synchronize access to mutable state, and how to secure it.

Kotlin and Java interoperability: Traps and gotchas

The parts of Kotlin and Java interoperability that might be surprising or counterintuitive.

Kotlin and Java interoperability: Useful annotations

Learn about useful Kotlin annotations, that decide that it is compiled to on JVM.

Kotlin and Java interoperability: Properties and annotations

Kotlin property is Java getter, setter, field and possibly more. So what to do, when you need to annotate or use a specific JVM element?

Kotlin and Java interoperability: Types

See surprising transitions that happens on types when you interoperate between Kotlin and Java.

Advanced Kotlin is finally ready!

Learn about our recently published book dedicated to the advanced Kotlin features.

Objects in Kotlin

What is object expression, object declaration and companion objects, and how we use them.

Books for 2023 company workshops attendees promotion

Our special promotion for company workshops organised in 2023.

Kotlin Contracts

Practical review of Kotlin Contracts - a feature we often use, without knowing about it.

Eliminating coroutine races

How to make one coroutine await for another coroutine or flow subscription.

Lindy effect in surnames problem

Using programming to simulate a problem of the number of surnames in population and observing Lindy effect.

The beauty of Kotlin type system

How type system makes Kotlin so flexible, safe, and intuitive.

Understanding Flow

We will explore how flow and its processing really works.

The second edition of Kotlin Coroutines: Deep Dive book is finally ready!

Learn about the new release of the famous book about Kotlin Coroutines.

Why you should consider migrating your Gradle scripts to Kotlin DSL

Discover the benefits of migrating your Gradle scripts to Kotlin DSL and streamline your development process.

Map as a property delegate

How do we use Map as a property delegate, and why the result of a famous puzzler should not be surprising.

Observable and Vetoable delegates

What are observable and vetoable delegates, and what are their real-life use cases.

Best practices

Let's review the Kotlin Coroutines best practices.

Kotlin revolutionary announcement

Kotlin announcement that will change the way we all will write code.

Lazy property delegate

What is lazy delegate, and what are its real-life use cases.

Property delegation

What is property delegation, how does it work, and how can we implement our custom property delegate.

Nullability in Kotlin

How Kotlin null-safety works, and how can we deal with nullable values.

Interface Delegation

One of the least known Kotlin features, that can be sometimes found really useful.

Kotlin bites on Twitter 2

A collection of Kotlin bites of knowledge, in a form of tweets.

Basic values in Kotlin

Learn about the basic Kotlin values, types and operations.

Variance modifiers limitations

What limitations generic variance modifiers introduce, and how can we ignore them.

Covariant Nothing Object

The pattern we are all using, but no-one talks about it.

Kotlin Generic Variance Modifiers

What are out and in, and how do we use them without even knowing.

Enum classes in Kotlin

What are enum classes in Kotlin and how do we use them.

Operator overloading in Kotlin

How are operators defined for types in Kotlin, and how can we define our own operators.

The power of Kotlin for-loop

Learn about the amazing capabilities of Kotlin for-loop.

Kotlin bites on Twitter 1

A collection of Kotlin bites of knowledge, in a form of tweets.

Your first program in Kotlin

How to write your first program, how can we use it in real-life projects, and how to explore what Kotlin is compiled to.

Running Kotlin coroutines on Project Loom's virtual threads

How to use Project Loom to improve Coroutines performance.

A birds-eye view of Arrow: Data Immutability with Arrow Optics

Learn to use Arrow Optics to support working on immutable objects.

Kotlin Essentials book is finally ready!

Learn about our recently published book dedicated to the essential Kotlin features.

Marcin Moskała
Marcin Moskała12/16/2022

Functions in Kotlin

Learn about what functions can offer us in Kotlin.

Marcin Moskała
Marcin Moskała12/12/2022

Slowing down your code with Coroutines

How can we use coroutines to slow down our code, and why would we want to do that.

Kotlin Coroutines use cases introduction

Introducing a series of articles about common Kotlin Coroutines use cases.

A birds-eye view of Arrow: Error Handling

Learn about Error Handling in Arrow, end how to effectively work with Either.

Kotlin Coroutines use cases for Presentation/API/UI Layer

How do we use Kotlin Coroutines in the Presentation/API/UI Layer Layer, how do we create scope and start coroutines.

Marcin Moskała
Marcin Moskała11/30/2022

A birds-eye view of Arrow: working with function with Arrow Core

Learn about essential Arrow functions used for composition, memoization, recursion and functions generation.

Kotlin Coroutines use cases for Domain Layer

How do we use Kotlin Coroutines in the Domain Layer.

Marcin Moskała
Marcin Moskała11/24/2022

Kotlin Coroutines use cases for Data/Adapters Layer

How do we use Kotlin Coroutines in the Data/Adapters Layer, how do we use callback or blocking functions.

Marcin Moskała
Marcin Moskała11/15/2022

Functional Kotlin book is finally ready!

Learn about our recently published book dedicated to functional Kotlin features.

Effective Kotlin Item 10: Design for readability

Do we really want out applications concise, or do we rather want them readable?

Marcin Moskała
Marcin Moskała10/24/2022

Effective Kotlin Item 7: Prefer a nullable or Result result type when the lack of a result is possible

Why should we prefer to avoid throwing exceptions and using types to our advantage.

Marcin Moskała
Marcin Moskała10/19/2022

Effective Kotlin Item 5: Specify your expectations for arguments and state

How do we specify requirements and expectations in Kotlin.

Marcin Moskała
Marcin Moskała10/12/2022

Context receivers

All you need to know about the new and powerful Kotlin feature: context receivers.

Effective Kotlin Item 1: Limit mutability

Why it is so important to limit mutability, and how Kotlin supports it.

Scope functions

What is let, also, apply and with, and how to use them in our applications.

Type modelling in Kotlin

Type safety is undervalued in most software projects and causes enormous financial losses throughout the world. Changing a few bad habits can lead to more reliable software.

DSL type-safe builders

How to define type-safe DSL builders in Kotlin.

Lambda expressions

Let's learn how to use lambda expressions, what special support they have, and what traps they generate.

Object-oriented or functional? Two ways to see the world

The difference between the OOP and FP paradigms is deeply rooted in how we see the world. A few words on the philosophy of both approaches.

Essential programming nomenclature

Find out what you need to know, before you start writing documentations, books or articles about programming.

Function references

How do we reference functions in Kotlin, to replace lambda expressions. All functions, including constructors, getters, extensions and more.

Best Principles for Successful Test Automation (API and UI)

Aligning our testing activities with ISTQB standards helps us to perform efficiently and cope with project scope and deadlines. In this workshop we will go over software testing stages starting from definition to maintenance.

Mesut
Mesut6/14/2022

Leveraging AI in Software Testing

As AI is confronting us in our daily lives and it is improving the development activities by eliminating some manual efforts, it is beneficial to embrace in our tasks. We will see how we can utilize AI based algorithms in Software Testing.

Mesut
Mesut6/7/2022

Software Testing Standards (Aligned with ISTQB)

Aligning our testing activities with ISTQB standards helps us to perform efficiently and cope with project scope and deadlines. In this workshop we will go over software testing stages starting from definition to maintenance.

Mesut
Mesut5/31/2022

How to write a technical book?

A guide for writing technical books.

Persistent memory design choices and use-cases

Let's understand some design choices with persistent memory and use-cases of persistent memory.

Why is Kotlin your next Programming Language?

What is Kotlin, and why it should be your next programming language.

Persistent dictionary

Let's make our in-memory dictionary persistent and understand some concepts of PMDK.

Code or No-code?

What are the strong sides of code and no-code, and why do they constantly fight with each other.

Introducing persistent memory

Let's learn the basics of persistent memory, its characteristics, how it works and the beauty of byte addressability.

In-memory dictionary

Let's begin our journey to understand persistent memory by building an in-memory dictionary.

Persistent memory - Introduction

Do you want to learn about persistent memory? Join this journey to explore persistent memory and build a persistent dictionary.

Funny programming comics

A collection of funny comics for programmers.

Kotlin Coroutines: Deep Dive book is finally ready!

Learn about our recently published book dedicated to Kotlin Coroutines.

SharedFlow and StateFlow

Known as a replacement for Subject, LiveData, and many more. SharedFlow and StateFlow are powerful coroutines classes, every Kotlin developer should know.

Funny programming videos

A collection of funny videos for programmers.

Advent of Kotlin Solutions

Solutions to the Advent of Kotlin!

Advent of Kotlin: Week 4

Week 4 of the Advent of Kotlin: Parsing JSON

Marcin Moskała
Marcin Moskała12/21/2021

Advent of Kotlin: Week 3

Week 3 of the Advent of Kotlin: k-means clustering

Marcin Moskała
Marcin Moskała12/14/2021

Advent of Kotlin: Week 2

Week 2 of the Advent of Kotlin: Tree algorithms

Advent of Kotlin: Week 1: JSON stringify and possible value parentheses

Week 1 of the Advent of Kotlin: JSON stringify and possible well-formed parentheses

Variables point to objects

A basic feature, that is commonly misunderstood.

Marcin Moskała
Marcin Moskała11/17/2021

Testing Kotlin Coroutines

How we test Kotlin Coroutines, including common Android and backend cases.

Marcin Moskała
Marcin Moskała10/27/2021

Constructing a coroutine scope

How we generally define coroutine scope on Android and on the backend.

Marcin Moskała
Marcin Moskała10/13/2021

Effective Kotlin Item 56: Consider using groupingBy instead of groupBy

What Grouping is, and how groupingBy instead of groupBy can be a performance optimization.

Marcin Moskała
Marcin Moskała10/11/2021

Effective Kotlin Item 55: Consider associating elements to a map

How associateBy is useful to improve the performance of finding elements.

Effective Kotlin Item 54: Prefer Sequences for big collections with more than one processing step

What the difference between list and sequence processing is, and when each should be preferred.

Effective Kotlin Item 53: Eliminate obsolete object references

How to help our garbage collector and avoid memory leaks.

Effective Kotlin Item 52: Consider using inline value classes

What value classes are, how to use and inline them.

Coroutines under the hood

A deep dive into how suspension and continuations work under the hood.

Effective Kotlin Item 51: Use the inline modifier for functions with parameters of functional types

How inline functions work and why they can be so important for the performance of our application.

Effective Kotlin Item 47: Avoid unnecessary object creation

About the most essential rule of performance optimization.

Traits for testing in Kotlin

A trick needed when using traits for testing in Kotlin.

How does suspension work in Kotlin coroutines?

A deep explanation of how suspension works in Kotlin Coroutines.

Effective Kotlin Item 32: Consider factory functions instead of secondary constructors

What factory functions are and why they are so important patterns for object creation.

Effective Kotlin Item 46: Avoid member extensions

What member extensions are, how they are possible and why we should avoid using them.

Kt. Academy new logo: Phoenix

Why we decided to change our logo, and what is the symbolism of Phoenix.

Effective Kotlin Item 36: Prefer composition over inheritance

Years of OOP made us overuse inheritance. Instead, we should more often use a composition that is safer and more explicit. More often, but not always...