create a Class Factory to customize arguments for injected dependencies

[BurnzZ]

This issue aims to discuss customizable arguments to injected dependencies as proposed by @gatufo.

This is in-line with the idea proposed in https://github.com/scrapinghub/web-poet/issues/18.

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The idea is to create a Class Factory that allows us to have a finer control for creating the injected dependencies. Here's an example:

@attr.define
class JsonPage(WebPage):
   semantic_data: ClassFactory(JsonParser, library='json')

@attr.define
class AnotherJsonPage(WebPage):
   semantic_data: ClassFactory(JsonParser, library='demjson')

In the example above, the ClassFactory returns a class which points to the appropriate implementation of the JSON Parser. A class should be returned to comply with the type annotation format which is later used for type inference on andi's build plan.

[kmike]

I was thinking about syntax similar to Python's built-in typing - something like

@attr.define
class JsonPage(WebPage):
   semantic_data: JsonParser['json']

@attr.define
class AnotherJsonPage(WebPage):
   semantic_data: JsonParser['demjson']

[kmike]

We can also use Annotated from stdlib.

[Gallaecio]

Should we close this now that we started using Annotated?

[BurnzZ]

Yes we can 👍