StateReducer

StateReducer is a lightweight Kotlin Symbol Processing (KSP) tool that generates compile-time state reducer functions and copy helpers for deeply nested UI/domain data classes. Say goodbye to verbose .copy() calls in MVI/Unidirectional Data Flow architectures.

💡 Why StateReducer?

Updating deeply nested data classes in Unidirectional Data Flow (UDF) or MVI architectures using standard Kotlin .copy() is verbose, error-prone, and hard to read. StateReducer automates this boilerplate with type-safe, auto-generated updater functions.

🔴 Before (Standard Kotlin .copy())

// 1. Define your data class hierarchy
data class UiState(
    val user: User = User(),
    val isLoading: Boolean = false
)

data class User(
    val profile: Profile = Profile()
)

data class Profile(
    val settings: Settings = Settings()
)

data class Settings(
    val isDarkMode: Boolean = false
)

// 2. Updating a deeply nested property requires nesting multiple copy calls
val updatedState = currentState.copy(
    user = currentState.user.copy(
        profile = currentState.user.profile.copy(
            settings = currentState.user.profile.settings.copy(
                isDarkMode = true
            )
        )
    )
)

🟢 AFTER (With StateReducer)

// 1. Define your data class hierarchy with @GenerateUpdaters
@GenerateUpdaters
data class UiState(
    val user: User = User(),
    val isLoading: Boolean = false
)

@GenerateUpdaters
data class User(
    val profile: Profile = Profile()
)

@GenerateUpdaters
data class Profile(
    val settings: Settings = Settings()
)

data class Settings(
    val isDarkMode: Boolean = false
)

class MainViewModel : ViewModel() {
    
    private val _uiState = MutableStateFlow(UiState())
    val uiState: StateFlow<UiState> = _uiState.asStateFlow()

    // 2. Updating nested state cleanly with StateReducer inside _uiState.update { }
    fun toggleDarkMode(enabled: Boolean) {
        _uiState.update { currentState ->
            currentState.updateUser {
                updateProfile {
                    updateSettings {
                        updateIsDarkMode(enabled)
                    }
                }
            }
        }
    }
}

---

⚡ Key Features

• Boilerplate Elimination: Automatically generates type-safe updater extensions for Kotlin data classes.
• KSP-Powered: Fast compile-time generation with zero reflection cost at runtime.
• KMP Compatible: Works across Android, iOS, Desktop, and Web Kotlin Multiplatform targets.
• Gradle Plugin Included: Zero-overhead setup using our dedicated Gradle plugin.

---

🚀 Quick Setup

Prerequisites

• Kotlin: 2.3.0 or higher

1. Apply the Gradle Plugin

In your module's build.gradle.kts:

plugins {
    id("io.github.RahmaniReza.statereducer") version "1.0.7"
}