Is there a good article on using closures as function arguments?

Question

Swift

Learning Swift after working with PHP and Java for a long time.
Brains boil when trying to read the listings. Stumbling over Swift's specific syntactic sugar.

It's good that the argument can be taken out of brackets.
But then. } dopArg: { - and the next one went.

Ideally, something from a person who himself retrained to Swift. Perhaps not only for these moments.