[TYPO3-mvc] How to extend a model class from within another extension?

[Martin Kutschker]

Franz Koch schrieb:
> because of all the type declarations used all over the code, f.e.
> "function setFoo(Tx_ExtOld_Domain_Model_Foo $foo)" which will throw a
> error if a model Tx_ExtNew_Domain_Model_Foo is passed to it.

If Tx_ExtNew_Domain_Model_Foo is a child of Tx_ExtOld_Domain_Model_Foo this shouldn't result to any
error.

Sidenote: in the code of Extbase I found a few interfaces. Yet many method signatures use the
(default) class and not the interface. I wonder why.

Masi