[TYPO3-mvc] Best way to convert "tx_ext_domain_model_foo:1" into object?

[Tim Schoch | GSTALTIG]

Hello list
I know there must be a function to which I can pass a string like "tx_ext_domain_model_foo:1" to and recieve the populized object back.
Extbase does it, so I should be able to call it too, but I havn't found where it is done. It would be nice if someone could give me a hint.
Thanks, Tim