Sequences get prefix(while:) and drop(while:) methods
Sequences get prefix(while:) and drop(while:) methods 관련
Available from Swift 3.1
Two useful new methods have been added to the Sequence protocol: prefix(while:) and drop(while:). The former returns the longest subsequence that satisfies a predicate, which is a fancy way of saying that you give it a closure to run on every item, and it will go through all the elements in the sequence and return those that match the closure – but will stop as soon as it finds a non-matching element.
Let's take a look at a code example:
let names = ["Michael Jackson", "Michael Jordan", "Michael Caine", "Taylor Swift", "Adele Adkins", "Michael Douglas"]
let prefixed = names.prefix { $0.hasPrefix("Michael") }
print(prefixed)
That uses the hasPrefix() method to return the subsequence ["Michael Jackson", "Michael Jordan", "Michael Caine" – the first three elements in the sequence. It won't include "Michael Douglas", because that comes after the first non-Michael. If you wanted all the Michaels regardless of their position, you should use filter() instead.
The second new method, drop(while:) is effectively the opposite: it finds the longest subsequence that satisfies your predicate, then returns everything after it. For example:
let names = ["Michael Jackson", "Michael Jordan", "Michael Caine", "Taylor Swift", "Adele Adkins", "Michael Douglas"]
let dropped = names.drop { $0.hasPrefix("Michael") }
print(dropped)
That will return the subsequence ["Taylor Swift", "Adele Adkins", "Michael Douglas"] – everything after the initial Michaels.