Re: [PATCH 10/19] qapi/schema: make QAPISchemaArrayType.element_type non-Optional

[Markus Armbruster]

John Snow <jsnow@redhat.com> writes:

> This field should always be present and defined. Change this to be a
> runtime @property that can emit an error if it's called prior to
> check().
>
> This helps simplify typing by avoiding the need to interrogate the value
> for None at multiple callsites.
>
> RFC: Yes, this is a slightly different technique than the one I used for
> QAPISchemaObjectTypeMember.type;

In PATCH 04.

>                                  I think I prefer this one as being a
> little less hokey, but it is more SLOC. Dealer's choice for which style
> wins out -- now you have an example of both.

Thanks for letting us see both.

I believe all the extra lines accomplish is a different exception
RuntimeError with a custom message vs. plain AttributeError.

I don't think the more elaborate exception is worth the extra code.

> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  scripts/qapi/schema.py | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> index c9a194103e1..462acb2bb61 100644
> --- a/scripts/qapi/schema.py
> +++ b/scripts/qapi/schema.py
> @@ -366,7 +366,16 @@ def __init__(self, name, info, element_type):
>          super().__init__(name, info, None)
>          assert isinstance(element_type, str)
>          self._element_type_name = element_type
> -        self.element_type = None
> +        self._element_type: Optional[QAPISchemaType] = None
> +
> +    @property
> +    def element_type(self) -> QAPISchemaType:
> +        if self._element_type is None:
> +            raise RuntimeError(
> +                "QAPISchemaArray has no element_type until "
> +                "after check() has been run."
> +            )
> +        return self._element_type
>  
>      def need_has_if_optional(self):
>          # When FOO is an array, we still need has_FOO to distinguish
> @@ -375,7 +384,7 @@ def need_has_if_optional(self):
>  
>      def check(self, schema):
>          super().check(schema)
> -        self.element_type = schema.resolve_type(
> +        self._element_type = schema.resolve_type(
>              self._element_type_name, self.info,
>              self.info and self.info.defn_meta)
>          assert not isinstance(self.element_type, QAPISchemaArrayType)