From the Swift docs regarding closures (I would have used Haskell doc reference, but the Haskell docs are so esoteric and vague as to be nearly useless):

“A closure can capture constants and variables from the surrounding context in which it’s defined. The closure can then refer to and modify the values of those constants and variables from within its body, even if the original scope that defined the constants and variables no longer exists.”

https://docs.swift.org/swift-book/LanguageGuide/Closures.htm...