tsyringe interface noncompliance runtime demo

README.md

tsyringe isn't type-safe

• Token 'Greeter' is supposed to match Greeter (needs greet).
• We register WrongGreeter (only has sayHello).
• TypeScript passes (npx tsc --noEmit) because the string token is untyped.
• Runtime blows up: this.greeter.greet is not a function.

Run:

npm install
npx tsc --noEmit
npm run start

effect.ts

import { Context, Effect, Layer } from 'effect';

// Modern class-based Context.Tag pattern.
// The class IS the tag — no separate interface needed.
class Greeter extends Context.Tag('Greeter')<
  Greeter,
  { readonly greet: (name: string) => string }
>() {
  static Live = Layer.succeed(this, {
    greet: (name: string) => `Hello, ${name} (from Effect)`,
  });
}

// This would be a compile-time error:
// static Live = Layer.succeed(this, { sayHello: ... });

const program = Effect.gen(function* () {
  const greeter = yield* Greeter;
  return greeter.greet('tsyringe + Effect');
});

Effect.runPromise(Effect.provide(program, Greeter.Live)).then(console.log);

index.ts

import 'reflect-metadata';
import { container, inject, injectable } from 'tsyringe';

// Contract we want the container to satisfy.
interface Greeter {
  greet(name: string): string;
}

@injectable()
class WrongGreeter {
  // Does not implement Greeter.greet; wrong method name/signature.
  sayHello(name: string): string {
    return `Hello, ${name}. (from the wrong greeter)`;
  }
}

@injectable()
class App {
  constructor(@inject('Greeter') private readonly greeter: Greeter) {}

  run(): void {
    // At runtime this will explode, because the container hands us WrongGreeter.
    console.log(this.greeter.greet('tsyringe'));
  }
}

// Using a string token without generics means register() defaults to T = any,
// so TypeScript cannot tell that WrongGreeter does not satisfy Greeter.
container.register('Greeter', { useClass: WrongGreeter });

try {
  container.resolve(App).run();
} catch (error) {
  console.error('Runtime failure because the implementation does not satisfy Greeter:', error);
}