# sealed Published articles for sealed. This is one page of public article previews, not the complete archive. Follow Next page to continue. Summaries are not the original full articles. ## Call for testing: Restricting trait implementability and field mutability DevFeed: [Call for testing: Restricting trait implementability and field mutability]() Original publisher: [Read original article]() Author: Ryosuke Yamano Published: 2026-08-10T00:00:00Z Content type: article Language: en Sources: [Inside Rust Blog]() Topics: [Rust](), [Testing](), [Code]() Tags: [compiler](), [implementation](), [rust](), [scope](), [sealed](), [testing]() ### AI overview Rust RFC 3323, "Restrictions," is ready for testing on nightly Rust. It introduces impl_restriction for limiting where traits may be implemented and mut_restriction for limiting where fields may be mutated. ### Source excerpt We are excited to announce that RFC 3323 "Restrictions" is ready for testing on nightly Rust. In this post, we will briefly describe the features. If you are already familiar with them, you can skip ahead to the How can I help? section. The RFC is split into two features: impl_restriction and mut_restriction. What is impl_restriction? The impl_restriction feature allows explicit restriction of the scope in which a trait may be implemented. For example, consider a trait Foo with a method that we want users to be able to call, while preventing downstream crates from providing their own implementations. With this feature, we can write: #![feature(impl_restriction)] pub impl(crate) trait Foo { fn method(); } impl Foo for usize { fn method() {} } The impl(crate) restriction prevents Foo from being implemented outside the current crate. As with pub, other paths can also be specified, such as impl(super) or impl(in path). Without this feature, this use case is typically handled using the sealed trait pattern, which is described in the Rust API Guidelines. In short, this pattern defines a public Sealed trait inside a private module and makes it a supertrait of Foo. Because downstream crates cannot name Sealed, they cannot implement Foo. pub trait Foo: private::Sealed { fn method(); } // Implement `Foo` for selected types. impl Foo for usize { fn method() {} } mod private { pub trait Sealed {} // Implement `Sealed` for those same types, but no others. impl Sealed for usize {} } However, this pattern requires defining an additional Sealed trait. The new impl_restriction feature provides a more direct and concise way to express the same restriction. The feature also allows the compiler to produce a more direct error message when an implementation is attempted outside the permitted scope. For example, the following code: #![feature(impl_restriction)] pub mod foo { pub mod bar { pub(crate) impl(super) trait Foo {} } // `Foo` may be implemented here. impl bar::Foo for i8 {} } // ## Nice and Naughty Cases of Pattern Matching DevFeed: [Nice and Naughty Cases of Pattern Matching]() Original publisher: [Read original article]() Author: Cay Horstmann Published: 2025-12-08T02:02:26Z Content type: article Language: en Sources: [Java Advent Calendar]() Topics: [Java](), [Programming](), [Code]() Tags: [2025](), [article](), [enums](), [exhaustive](), [expression](), [interfaces](), [java](), [java-language](), [pattern-matching](), [patterns](), [programming](), [sealed](), [statement](), [syntax](), [types]() ### AI overview This article examines Java pattern matching in switch and instanceof, explaining when it fits data-oriented programming, when it becomes an antipattern, and how it interacts with legacy behavior. It uses sealed interfaces, records, enums, and JSON values to illustrate exhaustive pattern matching. ### Source excerpt Since Java 14, the Java switch and instanceof statements have been enhanced, in multiple phases, to support pattern matching and a "data-oriented" programming style. In this article, I explore when this programming style is beneficial, and why. I look at the sweet spot of perfect pattern usage, absolute antipatterns where it should not be used, [...] The post Nice and Naughty Cases of Pattern Matching appeared first on JVM Advent. ## Automating Exhaustive Branch Coverage for Sealed Types in Kotlin DevFeed: [Automating Exhaustive Branch Coverage for Sealed Types in Kotlin]() Original publisher: [Read original article]() Author: Sean Amos Published: 2025-11-20T16:33:33Z Content type: tutorial Language: en Sources: [Wealthfront]() Topics: [Kotlin](), [Testing](), [Unit testing](), [test-coverage](), [Code quality]() Tags: [android](), [automation](), [code](), [code-quality](), [exhaustive](), [kotlin](), [sealed](), [sealed-classes](), [subtype](), [test-coverage](), [testing](), [unit-testing](), [wealthfront-engineering]() ### AI overview This article explains how to build an Exhaustive Test Runner for Kotlin sealed classes and interfaces. The approach ensures that functions accepting sealed parameters have at least one unit test for each subtype, including future subtypes added to the hierarchy. ### Source excerpt We take code correctness and code quality seriously at Wealthfront. One of the most effective ways we ensure that our code is correct is through rigorous unit testing and strong typing. In Kotlin, sealed classes and sealed interfaces offer a powerful tool to model restricted class hierarchies. They provide strong guarantees about the types in... Read more ## Why building from source matters DevFeed: [Why building from source matters]() Original publisher: [Read original article]() Published: 2025-11-13T00:00:00Z Content type: article Language: en Sources: [Chainguard: Unchained]() Topics: [chainguard](), [open-source-security](), [Security](), [Open Source](), [Software](), [Library](), [Compiler](), [virtual machines]() Tags: [binaries](), [building](), [building-from-source-approach](), [chainguard](), [chainguard-containers](), [chainguard-libraries](), [chainguard-open-source](), [chainguard-os](), [chainguard-vms](), [dependency](), [engineering](), [open-source](), [sealed](), [security](), [signing](), [source](), [supply-chain](), [trust]() ### AI overview Chainguard explains why building software from upstream source code can improve control and traceability in software supply chains. The article describes compiling packages and dependencies in a hermetic, network-isolated environment, then signing and attesting the resulting artifacts. ### Source excerpt Chainguard SVP of Engineering Dustin Kirkland discusses why Chainguard builds every package, library, and image directly from source and why the approach works. ## Sealed Types DevFeed: [Sealed Types]() Original publisher: [Read original article]() Author: author@typealias.com (Dave Leeds) Published: 2024-01-16T00:00:00Z Content type: tutorial Language: en Sources: [Dave Leeds on Kotlin - typealias.com]() Topics: [Kotlin](), [interfaces]() Tags: [classes](), [enum](), [exhaustive](), [exhaustive-matching](), [interfaces](), [introduction](), [kotlin](), [learn-to-program](), [programming](), [sealed](), [sealed-class](), [sealed-interface](), [subtype](), [types](), [when-conditional](), [when-expression]() ### AI overview A tutorial chapter explains how Kotlin sealed interfaces and classes restrict the set of possible types, helping ensure that all possibilities are handled in a when expression. ### Source excerpt In Chapter 5, we saw how limiting our options can be a good thing. In that chapter, we used enum classes to limit our values, which allows Kotlin to ensure that we account for all possibilities in a when expression. We can get a similar benefit for our types by using sealed interfaces and classes. In this chapter, we'll visit Cecil's Ice Shop to learn all about sealed types. Let's get started! ## Sealed Generics and SKIE - Paul Hawke DevFeed: [Sealed Generics and SKIE - Paul Hawke]() Original publisher: [Read original article]() Published: 2023-10-10T00:00:00Z Content type: tutorial Language: en Sources: [Touchlab | Enterprise Mobile Innovation & Development]() Topics: [Kotlin](), [generics](), [Swift](), [classes](), [Xcode]() Tags: [apis](), [classes](), [generics](), [kmp](), [kotlin](), [kotlin-multiplatform](), [sealed](), [sealed-classes](), [skie](), [swift](), [type](), [xcode]() ### AI overview This tutorial explores how SKIE improves the use of Kotlin sealed classes with generics when exposing Kotlin Multiplatform code to Swift. It discusses type discovery in Xcode, Swift interoperability, and concurrency-related code paths. ### Source excerpt Sealed Classes and Generics are both very useful for Kotlin APIs, and very painful with KMP and Swift. One of SKIE's lesser known benefits is the restoration of using Sealed Classes with generics, along with proper type discovery in Xcode. ## Touchlab Open Source Updates - Sep 2023 - Touchlab Engineering DevFeed: [Touchlab Open Source Updates - Sep 2023 - Touchlab Engineering]() Original publisher: [Read original article]() Published: 2023-09-19T23:33:27Z Content type: news Language: en Sources: [Touchlab | Enterprise Mobile Innovation & Development]() Topics: [multiplatform](), [Kotlin](), [iOS](), [Coroutines](), [Logging](), [Crashlytics](), [Code]() Tags: [class](), [concurrency](), [coroutines](), [crashlytics](), [default-parameters](), [engineering](), [enums](), [ios](), [kmp](), [kotlin](), [logging](), [multiplatform](), [open-source](), [sealed](), [updates]() ### AI overview Touchlab reports open-source updates for Kotlin Multiplatform, including SKIE improvements for Kotlin-to-iOS interfaces, the Kermit 2.0 release, CrashKiOS updates, and Stately 2.0 concurrency features. ### Source excerpt Touchlab has pushed some major open source updates over the past few weeks that will have an impact on how teams use KMP, and on KMP adoption overall. Here are the highlights. ## Sealed classes and interfaces in Kotlin DevFeed: [Sealed classes and interfaces in Kotlin]() Original publisher: [Read original article]() Published: 2023-09-04T00:01:00Z Content type: tutorial Language: en Sources: [Kt. Academy]() Topics: [Kotlin](), [sealed class](), [sealed interface](), [interface](), [abstract class](), [Inheritance](), [Polymorphism]() Tags: [inheritance](), [interface](), [kotlin](), [polymorphism](), [sealed](), [sealed-classes](), [sealed-interface](), [workshop-learning-programming]() ### AI overview This Kotlin tutorial explains sealed classes and sealed interfaces as restricted hierarchies whose direct subclasses are controlled. It contrasts them with regular interfaces and abstract classes, describes their package and module requirements, and explains their use in exhaustive expressions. ### Source excerpt What are sealed classes and interfaces in Kotlin and how do we use them. ## Class Modifiers in Dart: Sealed, Interface, Base DevFeed: [Class Modifiers in Dart: Sealed, Interface, Base]() Original publisher: [Read original article]() Author: Marvin März Published: 2023-06-23T11:29:43Z Content type: tutorial Language: en Sources: [QuickBird Studios Blog]() Topics: [Dart](), [Object-oriented programming (OOP)]() Tags: [abstract-class](), [class](), [classes](), [dart](), [flutter](), [implementation](), [interface](), [oop](), [pattern-matching](), [post](), [sealed](), [sealed-interface]() ### AI overview This tutorial explains Dart 3 class modifiers, including the newly introduced sealed, interface, final, and base modifiers and changes to existing modifiers. It describes how modifiers control whether classes can be extended, mixed in, constructed, or implemented, and discusses their practical use cases. ### Source excerpt With Dart 3 the class modifiers sealed, interface, final and base were introduced into the Dart language. They also updated how existing ones work. In this article, we show you why this change was made and how those new modifiers work. The post Class Modifiers in Dart: Sealed, Interface, Base appeared first on QuickBird Studios. ## Sealed classes in Kotlin DevFeed: [Sealed classes in Kotlin]() Original publisher: [Read original article]() Author: Florian Garcia Published: 2022-09-26T13:51:32Z Content type: tutorial Language: en Sources: [betclic-tech - Medium]() Topics: [Kotlin](), [interfaces](), [Inheritance](), [Code](), [Exception]() Tags: [classes](), [code](), [exception](), [inheritance](), [interfaces](), [kotlin](), [sealed](), [sealed-classes]() ### AI overview A tutorial explaining how Kotlin sealed classes and interfaces represent restricted class hierarchies. It shows how they help the compiler identify all supported cases and avoid missing-case handling when the hierarchy changes. ### Source excerpt In this article, we will talk about sealed classes and interfaces. What they are, what problem they solve and how we can leverage this in real life. The problem Let's take the following code: https://medium.com/media/f1f04b5ee8f0bfc98d41cad1fbd803a2/href Our code only handles two types of animals (cats and dogs). But the compiled code does not know that only those two types exist. This means we have to add this ugly else block in our when. This can be a real issue because you start to think about what to do in a situation that shouldn't exist but that will potentially exist in the future. For instance, say that tomorrow we add cows to the list of supported animals, the code will compile just fine because we have put the else block. We could change the else part to throw an exception but Kotlin does not have checked exceptions (so it's easy to forget to catch one), and thus we end up with runtime exceptions. That's a bit sad because we probably want to know at compile time that we need to handle this new case. Solution As you probably have guessed, the solution is sealed classes or interfaces. But what are they? From the Kotlin documentation: Sealed classes and interfaces represent restricted class hierarchies that provide more control over inheritance. All direct subclasses of a sealed class are known at compile time. No other subclasses may appear after a module with the sealed class is compiled. For example, third-party clients can't extend your sealed class in their code. Thus, each instance of a sealed class has a type from a limited set that is known when this class is compiled. If rephrased, this means that we can define a bounded hierarchy. One of the important things to know when working with sealed classes is that you cannot instantiate the sealed class; thus only the leaves of the structure exist at runtime (but you can use the interface as a type). When we develop applications that are not libraries, it is pretty rare to allow an abstract class / interfac ## Sealed interfaces in Kotlin DevFeed: [Sealed interfaces in Kotlin]() Original publisher: [Read original article]() Author: Jorge Castillo Published: 2021-03-06T10:00:00Z Content type: tutorial Language: en Sources: [👨💻 Jorge Castillo]() Topics: [Kotlin](), [interfaces](), [Compiler](), [Library](), [enum]() Tags: [enum](), [interface](), [kotlin](), [kotlin-compiler](), [sealed](), [sealed-class]() ### AI overview An overview of experimental sealed interfaces planned for Kotlin 1.5. The article explains relaxed subclass-location restrictions, allowing implementations in different files within the same module, and discusses why sealed interfaces can cover cases that sealed classes cannot, including enums implementing interfaces and types belonging to multiple sealed hierarchies. ### Source excerpt Short overview of the sealed interfaces coming up in Kotlin 1.5. ## Sealed goodies coming in Kotlin 1.5 DevFeed: [Sealed goodies coming in Kotlin 1.5]() Original publisher: [Read original article]() Author: Márton Braun Published: 2021-01-19T14:00:00Z Content type: article Language: en Sources: [zsmb.co]() Topics: [Kotlin](), [interfaces](), [Inheritance]() Tags: [android](), [classes](), [inheritance](), [interfaces](), [kotlin](), [marton-braun](), [pattern-matching](), [preview](), [sealed](), [sealed-classes](), [zsmb](), [zsmb-co](), [zsmb13](), [zsmbco]() ### AI overview This article explains Kotlin sealed classes and previews planned Kotlin 1.5 improvements, including relaxed inheritance restrictions and the introduction of sealed interfaces. It also discusses interoperability with newer Java sealed constructs. ### Source excerpt Kotlin 1.5 will bring exciting new features, among them improvements to sealed classes and an introduction of sealed interfaces. Let's take a look at what that will look like! ## Abstracting Kotlin Sealed Classes DevFeed: [Abstracting Kotlin Sealed Classes]() Original publisher: [Read original article]() Author: Artur Dryomov Published: 2019-06-04T00:00:00Z Content type: article Language: en Sources: [Artur Dryomov]() Topics: [Kotlin](), [Polymorphism](), [Refactoring](), [Java]() Tags: [bytecode](), [java](), [kotlin](), [models](), [polymorphism](), [properties](), [refactoring](), [sealed](), [sealed-classes]() ### AI overview This article examines ways to declare common properties in Kotlin sealed class hierarchies. It compares approaches involving type declarations, constructors, and separate Java-rooted abstractions, including their ergonomics and generated bytecode implications. ### Source excerpt Things tend to be similar. Cars and bikes are different for sure but both have wheels, engines, exhaust systems and so on. Such similarities between models are usually described using basic polymorphism in virtual domain modeling. Kotlin makes this process a bit more pragmatic using sealed class declarations. Specifying type hierarchies using sealed classes is simple, but what about declaring common properties? Fortunately or not there are multiple ways to achieve this -- partially because of the Java baggage. Which one is the best? ## The Dog Riddle DevFeed: [The Dog Riddle]() Original publisher: [Read original article]() Author: Márton Braun Published: 2019-04-25T18:00:00Z Content type: article Language: en Sources: [zsmb.co]() Topics: [Kotlin](), [API](), [Code]() Tags: [android](), [api](), [api-design](), [code](), [kotlin](), [marton-braun](), [sealed](), [sealed-class](), [zsmb](), [zsmb-co](), [zsmb13](), [zsmbco]() ### AI overview A Kotlin API design challenge asks readers to model cats and dogs, including dogs with optional breeds, while enforcing valid syntax and predictable instance creation. The article discusses submitted solutions, a common singleton-related pitfall, sealed hierarchies, and exhaustive expressions. ### Source excerpt A fun little challenge in Kotlin API design. Give it a try!