@inject_fields decorator for __init__

[smarie]

Feature 3

user writes his own but does not want to write all the argument names so he could use a special variable fields in the constructor, and anywhere in his constructor do fields.assign() or fields.init().

        @inject_fields(height, color)
        def __init__(self, fields):
            fields.init()

pros:

• you can use autocompletion so it is fast to type the decorators
• you only declare the fields that you need, in the order that you like
• you control when init happens
• you can easily debug what happens during field initialization

cons:

• it does not seem possible to have @inject_fields work without arguments, or even with the class as argument, to say "use all fields from class", except if we allow introspection to be used. Indeed, at the time where the __init__ method is decorated, it is not yet bound to the class. EDIT actually it is possible: we can create a non-data descriptor on the class (this was inspired by this link).

Originally posted by @smarie in #2 (comment)