For users upgrading from 2.3 to 2.7, there are a lot of deprecation warnings around ChoiceList, SimpleChoiceList and ChoiceListInterface. The recommendation is to use ArrayChoiceList instead. However, there currently isn't any documentation about how to use that, and the current 2.7 documentation suggests using the deprecated ChoiceList. See http://symfony.com/doc/current/reference/forms/types/choice.html#choice-list

This is a very complicated area of Symfony forms which has been in a bit of flux due to potential API changes, so it would be good to have some examples of usage.

I'd update the docs myself, but I haven't figured out how ArrayChoiceList actually works yet.