Bringing toSelf() to the next level

[osi-oswald]

I am aware of #500, #505 and inversify-binding-decorators. Nonetheless, I would love to have a container option fallbackToSelf at hand.

Motivation:

• not having to type implicit bindings
• same convenience as in angular: only @Injectable() and @Inject() are necessary (bindings are not mandatory)

What it does / How it behaves:

• Whenever the container would otherwise throw "No matching bindings found..." for an @Injectable() class, it will use itself as the binding and therefore not throw at that point
• This "fallback" behavior runs in the "planning" phase, meaning after any manual binding definitions
  • @Injectable() and container.bind will not be affected at all by this container option
  • container.get method will need changes (specifically the planning logic)
• @provide decorator of inversify-binding-decorators does not do the job, because the container must be known at "decorating" phase (which I consider an antipattern btw)
• If possible, fallbackToSelf will not add a binding at any point, but rather fall back to the "toSelf()" binding if no binding is defined for an @Injectable() class

Some examples:

@injectable() class A {}
@injectable() class B { constructor(a: A) {} }
@injectable() class AFake {}
class C {}

const container1 = new Container({fallbackToSelf: true});
container1.get(A); // does not throw, returns transient A
container1.get(B); // does not throw, returns transient B

const container2 = new Container({defaultScope: 'Singleton', fallbackToSelf: true});
container2.get(A); // does not throw, returns singleton A
container2.get(B); // does not throw, returns singleton B

const container3 = new Container({fallbackToSelf: true});
container3.bind(A).toSelf().inSingletonScope();
container3.get(A); // returns singleton A because of explicit binding
container3.get(B); // does not throw, returns transient B with singleton A

const container4 = new Container({fallbackToSelf: true});
container4.bind(A).to(AFake);
container4.get(A); // returns transient AFake because of explicit binding
container4.get(B); // does not throw, returns transient B with transient AFake

const container5 = new Container({fallbackToSelf: true});
container5.get(C): // still throws -> No matching bindings found

I tried to do this somehow with a middleware, but I think it is not possible.