Check how iPOPO decorators behave with Data Classes

[tcalmant]

Python 3.7 introduces Data Classes (PEP-557).

Before the next release of iPOPO, it will be necessary to

1. test if our decorators behave correctly with this kind of class
2. check if there are some constraints (decorators ordering, ...)
3. add some hints in the documentation about this special case

[tcalmant]

After some tests, here are some notes about Data Classes and iPOPO. The test files are in tests/dataclasses/, and are not executed during unit tests: they would only work for Python 3.7 and 3.6 with the dataclasses package.

Important notes

• All fields of the Data Class must have a default value. This will let the decorator generate an __init__ method without required argument, which is a requirement for iPOPO.
• If the init=False argument is given to @dataclass, it is necessary to implement your own __init__, defining all fields, otherwise generated methods like __repr__ won't work.

Good to know

• Injected fields (@Property, @Requires, ...) will lose their default value, as the iPOPO decorator redefines them. Other fields are not touched at all.
• the @dataclass decorator can be used before or after the iPOPO decorators