Ruby's take_while ported using a Swift 2.0 protocol extension

take_while.swift

var source = [1, 2, 3, 4, 5, 0]

extension CollectionType {
    func takeWhile(@noescape condition: (Self.Generator.Element) -> Bool) -> [Self.Generator.Element] {
        var returnArray : [Self.Generator.Element] = []
        
        for x in self {
            guard condition(x) else { break }

            returnArray.append(x)
        }
        
        return returnArray
    }
}

let target = source.takeWhile { $0 < 3 }

print(target) // [1, 2]