The Fetch class is responsible for moving data in and out of some
collection in the execution environment. The Fetch class is templated
with a pair of tags (the type of fetch and the aspect) that control the
mechanism used for the fetch.
The Transport class is responsible for moving data from the control
environment to the execution environment. (Actually, it might be more
accurate to say it gets the execution environment associated with a
given control object.) The Transport class is templated with a tag that
controls the mechanism used for the transport.
Whenever creating a functor to be launched in the execution environment
using the device adapter Schedule algorithm, you had to also create a
couple of methods to handle error message buffers. For convenience, lots
of code started to just inherit from WorkletBase. Although this worked,
it was a misnomer (and might cause problems in the future if worklets
later require different things from its base). To get around this
problem, add a FunctorBase class that is intended to be used as the
superclass to functors called with Schedule.
