TODO

TODO:
- ensure that memoization works properly with partial injection
- improve DirectlyPassingInjectedArgsError
- auto-require provider method args
- allow testing that bindings exist to allow object to be provided
- move obj_provider into injection_context, so that provisers only have one arg?
- describe features specifically omitted, e.g.,
  - circular injection
  - scope annotations on classes
- figure out whether/how Pinject works with inheritance
- make provider bindings inject a provider that has the correct signature (difficult!)

Maybe TODO:
- make @inject complain if not applied to initializer or binding spec method
    (doesn't seem possible: method passed to decorator has type 'function' and
    seemingly no info about the class in which it's defined)
- allow object_graph.provide('arg name')?
- standard tests for scopes (reentrant? thread-safe?), annotations (eq?
     hash?), etc.
- change default scope back to prototype?
- eager singletons
- find modules on PYTHONPATH instead of having to import them
- automatically instantiate the concrete subclass of an interface?
    (use abc module)
- visual graph of created objects

Questions:
- How should I deal with someone wanting to instantiate a class in a scope,
    without using an arg name in between?  Scopes apply to binding keys,
    which are arg names, not classes.  Is it going to be harmful if you
    can't instantiate a class directly in a scope?  I don't think so, but
    I'm not sure.  It makes some things awkward, like a special scope from
    which it's OK to inject objects from any scope.  Maybe the main
    ObjectGraph method should be wrap() instead of provide_class()??
- Why should @inject apply to __init__() rather than the class?