Dependency Injection

Pencel uses a lightweight DI container for core compiler components only. Not for plugins or application code.

Why DI?

Singleton pattern – One instance per compilation
Automatic wiring – Services find dependencies without manual setup
Testability – Register mock instances for testing
Circular dependency detection – Catches configuration errors early

Usage

All core services use inject() to retrieve dependencies:

import { inject } from "../core/container.ts";
import { Config } from "../config.ts";

export class MyService {
  readonly #config = inject(Config);
  readonly #plugins = inject(Plugins);
}

Key: Private readonly fields, no constructor parameters, no decorators.

API

inject<T>(ctor) – Get or create singleton instance
injectLazy<T>(ctor) – Returns function that calls inject() when invoked
register<T>(ctor, instance) – Manually register pre-created instance (testing)
clear() – Reset all instances (between test runs)

Scope

✅ Used for:

Program, SourceFiles, FileProcessor, Compiler
IRRI, Plugins, FileWriter, SourcePrinter

❌ NOT used for:

User plugins (receive via hook parameters)
Framework adapters
Application code

Implementation

Simple and synchronous:

instances Map – Stores singleton instances
instantiating Set – Tracks services being constructed (detects cycles)
pending Map – Tracks async initialization

Each service creates exactly one instance per compilation, shared across all consumers.