Function Policy

Policy<T extends ClassType = ClassType>(alias?: string): ClassDecorator
Declare a class as a policy.

Three statements in one, which is why nothing has to be wired by hand:
1. It is a service. The container builds it, as a singleton, so its constructor is auto-wired like any other class: a repository, a client, a translator, whatever it destructures is resolved for it. That is what lets a policy depend on the application instead of on constants.
2. It is reachable by name. The alias is bound as policy:<name>, prefixed on purpose: an application is free to bind its own service under a plain word, and a declaration named after a domain concept must not compete for that name.
3. It activates the module. The blueprint comes with the decorator, so declaring this is the whole setup, and a route naming it resolves to this class.
Type Parameters
- T extends ClassType = ClassType
Parameters
- Optionalalias: string
  The name a route refers to it by. Defaults to the class name.
Returns ClassDecorator
A class decorator.
Example
```
@Policy('post')
export class PostPolicy {
  constructor (private readonly teams: TeamRepository) {}
  update (user: User, post: Post): boolean { return post.authorId === user.id }
}
```