Using default arguments when nothing is injected

Using NewType (or Key) is a great way to inject configuration into classes, but there are cases where there is a sane default that is rarely overridden. In these cases it would be nice to have a way to define the default value close to where it is used.

Injector currently does not consider default values unless @noninjectable is used, but @noninjectable does not allow configuration to be injected when the default is not to be used.

Is there a way to do this? If not, what are your thoughts on the topic?

The following is an example of how it would be useful:

SleepTime = NewType('SleepTime', float)


class WaitStrategy:

    @inject
    def __init__(self, sleep_time: SleepTime = 1.0) -> None:
        self._sleep_time = sleep_time

Start by examining the injector's handling of default arguments and the existing @noninjectable behavior described in the issue. Compare both paths against the WaitStrategy example and determine the intended API before making changes. Done means the default can be used while still allowing the dependency to be injected when configured, with behavior covered by appropriate tests.