Purity

What is this?

A Kotlin Compiler Plugin for determining and enforcing Pure and Readonly functions.

Why?

• Communicating and enforcing function intent
• Determining parallelizable calls (Pure functions are parallelizable with anything; Readonly are parallelizable with each other)

Installation + Basic Usage

Install the plugin by adding the following to your build.gradle.kts:

plugins {
    id("io.github.yairm210.purity-plugin") version "1.3.2"
}

dependencies {
  implementation("io.github.yairm210:purity-annotations:1.3.2")
}

Mark pure functions using @Pure, and readonly functions using @Readonly:

import yairm210.purity.annotations.Pure
import yairm210.purity.annotations.Readonly

@Pure
fun pureFunction(x: Int): Int {
    return x * 2
}

@Readonly
fun readonlyFunction(list: List<String>): Int {
    return list.size
}

Advanced usage

Further details are available in the documentation

Rules

• Pure functions may not:

  • Get or set external vars (vars created outside the function)
  • Call other non-pure functions

• Readonly functions may not:

  • Set external vars
  • Call other non-readonly functions (pure functions are considered readonly as well)

Any violation of these rules creates a compilation error.

Limitations

• All getters are assumed to not be state-changing
• All constructors are assumed to be pure - to change state only of the instance being created

Development

Development instructions here

Acknowledgments

Projects that helped me understand how to setup the project:

• Foso/KotlinCompilerPluginExample
• bnorm/kotlin-power-assert