extra.ts

// extra constraint
function action<TContext extends MyContext>(handler: (arg: TContext) => void): Function {
	return function (object: object, aub: any, descriptor: any) {
		if (!object.hasOwnProperty('getContext')) {
			throw new Error("Can't bind @action to class which don't implement 'getContext' method");
		}

		// @ts-ignore
		const ctx = object.getContext();

		console.log(`listening to: ${handler(ctx)}`);
	};
}

interface ContextProvider<T> {
	getContext(): T;
}

type MyContext = {
	some_id: number;
};

class Controller implements ContextProvider<MyContext> {
	@action(ctx => `event:${ctx.some_id}`)
	public eventHandler(message: any) {
		console.log('My event handler', message);
	}

	getContext(): MyContext {
		return { some_id: 6 };
	}
}

type AnotherContext = { another_id: number };

class Controller2 implements ContextProvider<AnotherContext> {
	// This shouldn't compile, since context here is `AnotherContext` and it doesn't have `some_id` property on it
	@action(ctx => `event:${ctx.some_id}`)
	public eventHandler(message: any) {
		console.log('My event handler', message);
	}

	getContext(): AnotherContext {
		return { another_id: 6 };
	}
}