Commit 9345562

Use composition

When writing a driver, take in objects that provide the functionality you need

rather than taking their arguments and constructing them yourself or subclassing

a parent class with functionality. This technique is known as composition and

leads to code that is more flexible and testable than traditional inheritance.

.. seealso:: `Wikipedia <https://en.wikipedia.org/wiki/Dependency_inversion_principle>`_

has more information on "dependency inversion".

For example, if you are writing a driver for an I2C device, then take in an I2C

object instead of the pins themselves. This allows the calling code to provide

any object with the appropriate methods such as an I2C expansion board.

Another example is to expect a `DigitalInOut` for a pin to toggle instead of a

`microcontroller.Pin` from `board`. Taking in the `~microcontroller.Pin` object

alone would limit the driver to pins on the actual microcontroller instead of pins

provided by another driver such as an IO expander.