kt.dart — Kotlin like collections for your Flutter business logic
No matter how great Flutter is, using Dart feels like a step backwards when coming from Kotlin. I understand the reasoning why Dart was chosen as Flutters language but I miss Kotlins feature rich standard library. That’s why I decided to port it to Dart. Welcome kt.dart!
kt.dart doesn’t introduce new language features but it would definitely benefit from some. That’s why I invite you to upvote some of my favorites Dart language proposals: Extension Methods, Optional Semicolons, Non-Nullable types, Destructuring Declarations, Data Classes
Dart’s missing high-level collections for business logic
The most common collection in nearly every programming language is the array. Dart doesn’t have arrays, Dart arrays are Lists. And Dart’s Lists are amazing compared to Java’s
Array. But is such a comparison justifiable? Shouldn’t Dart’s
List better be compared with Java’s
ArrayList or Kotlins
Neither of those comparisons are fair. The most important aspect is that there is a right tool for the job.
My job is to write business logic and SDK with stable APIs. This is much more challenging in Dart compared to Kotlin. Especially Dart’s collections aren’t perfect for the job. That’s why I ported Kotlins high-level collections to Dart, allow me to write better APIs.
Before I jump into
kt.darts API, I’d like to show where Dart’s collections are lacking compared to kotlins collections:
Using Kotlin made me used to immutability. My entities are immutable (data classes) and so are the Lists I return from my APIs. Immutable entities aren’t a problem in Dart. But a immutable
List has the same API as a modifiable
List. Consumers might expect to be able to mutate a immutable
List. There is no compiler warning, it crashes at runtime.
There is also no way to test if a
List is modifiable or not. Unlike Kotlin, Dart doesn’t differentiate between
Comparing two Dart collections (
Map) doesn’t compare their contents, it only checks their identity. Dart offers a solution: The equality functions in the
But Dart’s collections don’t use
DeepCollectionEquality for their equals checks internally, which makes methods like
Dart doesn’t offer collections which are deep equal and differentiate between immutable and mutable collections. Since it doesn’t exists kt.dart is here to fill the void.
kt_dart | Dart Package
kt_dart Dart package - This project is a port of kotlin-stdlib for Dart/Flutter projects. It includes collections…
kt.darts collection package offers immutable collections (
KtMap) with a correct equals implementation.
This is similar to built_value, but it doesn’t stop there. kt.dart collections also offers mutable types. Only the mutable types offer mutation methods. Nobody can accidentally try to mutate an immutable collection.
KtIterable doesn’t extend Dart’s Iterable
Unlike built_value, kt.dart collections don’t extend Dart’s
Iterable. The reason for this is that Dart’s naming of methods is uncommon. Modern languages (Kotlin, Swift, TypeScript) all named their
Iterable methods the same (
filter, …). This helps a lot when working with developers from different platforms. Dart’s
where is less common.
The minor downside of not extending
Iterable is that for loops don’t work out of the box. To solve this, each
KtIterable exposes a Dart
iter. A for loop then looks like this:
Additionally, kt.dart collections comes with over 150 methods out of the box. All of them can be easily discovered via auto-completion.
Notice that collections can be created by either a function
listOf(1, 2, 3),
listFrom([1, 2, 3]) (Kotlin style) or a constructor call
List.of(1, 2, 3),
List.from([1, 2, 3]) (Dart style). Both versions are equally supported the usage depends on your personal taste.
Just the beginning
This is just the beginning of kt.dart. The
collection module is the first (and most important) part. But I can already think about more modules. For example
If you have questions or feedback, let me know! Hit me on Twitter for a quick chat. I’m super interested!
Pascal Welsch (@passsy) | Twitter
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