swift - swift 中 .successor() 的替代品？

Question

let greeting = "Guten Tag!"

greeting[greeting.startIndex.successor()] 
// "u"

greeting[greeting.startIndex.successor().successor().successor()]
// "e"

除了多次编写 .successor() 之外，还有其他选择吗？

Answer 1

在Swift 2.0中，这是advancedBy:

greeting[greeting.startIndex.advancedBy(3)]  // "e"

在Swift 1.2中:

greeting[advance(greeting.startIndex, 3)]  // "e"