Poko

Poko is a Kotlin compiler plugin that makes writing and maintaining data model classes for public APIs easy. Like with normal Kotlin data classes, all you have to do is provide properties in your class's primary constructor. With the @Poko annotation, this compiler plugin automatically generates toString, equals, and hashCode functions.

Use

Mark your class as a @Poko class instead of a data class:

@Poko class MyData(
    val int: Int,
    val requiredString: String,
    val optionalString: String?,
)

And enjoy the benefits of a readable toString and working equals and hashCode. Unlike normal data classes, no copy or componentN functions are generated.

Like normal data classes, Poko classes must have at least one property in their primary constructor. Non-property parameters in the primary constructor are ignored, as are non-constructor properties. Any of the three generated functions can be overridden manually, in which case Poko will not generate that function but will still generate the non-overridden functions. Using array properties is not recommended, and if they are used, it is recommended to override equals and hashCode manually.

Arrays

By default, Poko does nothing to inspect the contents of array properties. This aligns with data classes.

Poko consumers can change this behavior on a per-property basis with the @ArrayContentBased annotation. On properties of a typed array type, this annotation will generate a contentDeepEquals check. On properties of a primitive array type, this annotation will generate a contentEquals check. And on properties of type Any or of a generic type, this annotation will generate a when statement that disambiguates the many array types at runtime and uses the appropriate contentDeepEquals or contentEquals check. In all cases, the corresponding content-based hashCode and toString are generated for the property as well.

Using arrays as properties in data types is still not generally recommended: arrays are mutable, and mutating data can affect the results of equals and hashCode over time, which is generally unexpected. For this reason, @ArrayContentBased should only be used in very performance-sensitive APIs.

Annotation

By default, the dev.drewhamilton.poko.Poko annotation is used to mark classes for Poko generation. If you prefer, you can create a different annotation and supply it to the Gradle plugin.

apply plugin: "dev.drewhamilton.poko"
poko {
  pokoAnnotation.set "com.example.MyDataAnnotation"
}

Note that this only affects the primary marker annotation. Supplemental annotations such as @ArrayContentBased do not support customization.

Download

Poko is available on Maven Central. It is experimental, and the API may undergo breaking changes before version 1.0.0. Kotlin compiler plugins in general are experimental and new versions of Kotlin might break something in this compiler plugin.

Since the Kotlin compiler has frequent breaking changes, different versions of Kotlin are exclusively compatible with specific versions of Poko.

Snapshots of the development version are available in Sonatype's Snapshots repository.

To use Poko, apply the Gradle plugin in your project:

// Root project:
plugins {
    id("dev.drewhamilton.poko") apply false
}

// Per module:
plugins {
    id("dev.drewhamilton.poko")
}

*Versions prior to 0.7.0 use plugin name dev.drewhamilton.extracare.

To-do

• Generate an inner Builder class
• Propagate the constructor default values to the Builder
• Mark the constructor as private
• Generate a top-level DSL initializer
• Write an IDE plugin?
• Multiplatform support?

License

Copyright 2020 Drew Hamilton

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.