public interface DeferredSupplier<T>
A class that supplies objects of a single type. When used as a ConfigKey value,
the evaluation is deferred until getConfig() is called. The returned value will then
be coerced to the correct type.
Subsequent calls to getConfig will result in further calls to deferredProvider.get(),
rather than reusing the result. If you want to reuse the result, consider instead
using a Future.
Note that this functionality replaces the ues of Closure in brooklyn 0.4.0, which
served the same purpose.