Chain of Command does not support polymorphism

In an earlier post, I played around with Chain of Command to explain how it works in general.
This post will be more advanced. Chain of command does not support polymorphism. I have augmented 2 classes that are already in Parent-child relation and when I expected the child class’s extension method to be called, the parent was called instead.

Explanation through example

The 2 classes that I augmented are SalesInvoiceJournalPost and FormLetterJournalPost. Following is their class hierarchy:

When I post a sales invoice, another augmentation kicks in:

As formletterJournalPostGTE is of type SalesInvoiceJournalPost I expect that the method from SalesInvoiceJournalPost_PEP_Extension is called, but this is not the case. The method ‘formletterJournalPost_PEP_Extension.createInvoiceReporting_PEP(…)’ is called, but that is the extension of the parent class.

If I validate the type of ‘formLetterJournalPostGTE’, it is SalesInvoiceJournalPost:

The correct extension method was called.


Just be aware that polymorphism is not supported and use the ‘as’ keyword as a workaround in the cases when it helps.

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