string - Swift 如何使字符串右对齐

Question

如何使字符串右对齐？现在，我知道如何使用 stringByPaddingToLength 使字符串左对齐。有向右对齐的想法吗？

Answer 1

可能的实现(内联解释):

extension String {
    func stringByLeftPaddingToLength(newLength : Int) -> String {
        let length = self.characters.count
        if length < newLength {
            // Prepend `newLength - length` space characters:
            return String(count: newLength - length, repeatedValue: Character(" ")) + self
        } else {
            // Truncate to the rightmost `newLength` characters:
            return self.substringFromIndex(startIndex.advancedBy(length - newLength))
        }
    }
}

使用示例:

let s = "foo"
let padded = s.stringByLeftPaddingToLength(6)
print(">" + padded + "<")
// >   foo<

---

Swift 3 更新:

extension String {
    func stringByLeftPaddingTo(length newLength : Int) -> String {
        let length = self.characters.count
        if length < newLength {
            // Prepend `newLength - length` space characters:
            return String(repeating: " ", count: newLength - length) + self
        } else {
            // Truncate to the rightmost `newLength` characters:
            return self.substring(from: self.index(endIndex, offsetBy: -newLength))
        }
    }
}