🚇 Metro

A compile-time dependency injection framework for Kotlin Multiplatform, powered by a Kotlin compiler plugin.

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What is Metro?

Metro is a compile-time dependency injection framework that combines the best of Dagger, Anvil, and kotlin-inject into one cohesive solution.

Key Features:

• ✅ Compile-time validation – Catch dependency graph errors during compilation, not at runtime
• 🧩 FIR/IR code generation – No KAPT or KSP required, just a Kotlin compiler plugin
• 🎯 Kotlin-first API – Inspired by kotlin-inject with top-level function injection and optional dependencies
• 🗡️ Dagger-esque runtime – Lean generated code with familiar patterns
• ⚒️ Anvil-style aggregation – @ContributesTo, @ContributesBinding, and more
• 🌐 Multiplatform – Supports JVM, JS, Wasm, and Native targets
• 💡 Helpful diagnostics – Detailed error messages with actionable suggestions
• 🔗 Advanced interop – Migrate incrementally from Dagger, kotlin-inject, or Guice
• ⚡️ Fast - At build time, at runtime

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Quick Start

1. Apply the Gradle plugin:

plugins {
  id("dev.zacsweers.metro") version "<version>"
}

2. Define a dependency graph:

@DependencyGraph
interface AppGraph {
  val repository: UserRepository

  @Provides
  fun provideApi(): Api = ApiImpl()
}

@Inject
class UserRepository(private val api: Api)

3. Create and use the graph:

val graph = createGraph<AppGraph>()
val repository = graph.repository

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Documentation

📚 zacsweers.github.io/metro

Topic
Installation	Setup and configuration
Dependency Graphs	Define and create graphs
Provides	Provider functions and properties
Injection Types	Constructor, assisted, and member injection
Scopes	Scoping and lifecycle management
Aggregation	Anvil-style contributions across modules
Interop	Dagger, kotlin-inject, and Guice compatibility
Performance	Build and runtime performance
Compatibility	Supported Kotlin versions
FAQ	Frequently asked questions
API Docs	Generated KDocs

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Supported Platforms

Metro supports JVM, Android, JS, Wasm, and Native targets. The compiler plugin works with all Kotlin Multiplatform project types.

See the multiplatform docs for full details.

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License

Copyright (C) 2025 Zac Sweers

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

   https://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.