Re: [PATCH v4 08/14] qapi/introspect.py: create a typed 'Annotated' data strutcure

[Eduardo Habkost]

On Wed, Feb 03, 2021 at 03:47:36PM +0100, Markus Armbruster wrote:
> John Snow <jsnow@redhat.com> writes:
> 
> > Presently, we use a tuple to attach a dict containing annotations
> > (comments and compile-time conditionals) to a tree node. This is
> > undesirable because dicts are difficult to strongly type; promoting it
> > to a real class allows us to name the values and types of the
> > annotations we are expecting.
> >
> > In terms of typing, the Annotated<T> type serves as a generic container
> > where the annotated node's type is preserved, allowing for greater
> > specificity than we'd be able to provide without a generic.
> >
> > Signed-off-by: John Snow <jsnow@redhat.com>
[...]
> > +class Annotated(Generic[_NodeT]):
> > +    """
> > +    Annotated generally contains a SchemaInfo-like type (as a dict),
> > +    But it also used to wrap comments/ifconds around scalar leaf values,
> > +    for the benefit of features and enums.
> > +    """
> > +    # Remove after 3.7 adds @dataclass:
> 
> Make this
> 
>        # TODO Remove after Python 3.7 ...
> 
> to give us a fighting chance to remember.
> 
> > +    # pylint: disable=too-few-public-methods
> > +    def __init__(self, value: _NodeT, ifcond: Iterable[str],
> > +                 comment: Optional[str] = None):
> 
> Why not simply value: _value?

Example:
  x = C(1)
  y: C[int]
  y = C('x')  # mistake

Declaring value as _NodeT does:
- Make the inferred type of x be Annotated[int].
- Catch the mistake above.

-- 
Eduardo