[QUERY] Guide on customization, when polymorphic class be customized to be "abstract"

[weidongxu-microsoft]

Query/Question
Case #39109 (comment)

Service set the superclass to abstract. There the code of "fromJson" will no longer compile.

We need a guide on how to customize such case in azure-core serialization.

Why is this not a Bug or a feature Request?
A clear explanation of why is this not a bug or a feature request?

Setup (please complete the following information if applicable):

• OS: [e.g. iOS]
• IDE: [e.g. IntelliJ]
• Library/Libraries: [e.g. com.azure:azure-core:1.16.0 (groupId:artifactId:version)]

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[joshfree]

@alzimmermsft

[alzimmermsft]

To close this out, I don't think we should be customizing classes to be abstract anymore given the issues it causes, and the low value add making them abstract. Making them abstract doesn't really change behaviors meaningfully from them being non-final classes, as we don't generate abstract methods that subclasses need to implement.

So, in short, I'd say we stop customizing to abstract wholesale unless we fundamentally change how code is generated in the future to include abstract methods that subclasses need to implement.