Isn't that such that you can declare a dictionary or array as constant by using 'let' in the declaration? I think the designers wanted to avoid complicated annotations for constant the way it works in C++. Being able to use 'let' also seems to make collections available for matching in case statements. I recommend watching this[1] tutorial - the way switch/case works in Swift was really impressive to me.

[1] http://fitacular.com/blog/swift/2014/06/08/apple-ios-tutoria...