下面是一个代码片段，用n个字符分隔字符串:

//: A UIKit based Playground for presenting user interface

import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {
    override func loadView() {

        let str = String(charsPerLine: 5, "Hello World!")
        print(str) // "Hello\n Worl\nd!\n"

    }
}

extension String {

    init(charsPerLine:Int, _ str:String){

        self = ""
        var idx = 0
        for char in str {
            self += "\(char)"
            idx = idx + 1
            if idx == charsPerLine {
                self += "\n"
                idx = 0
            }
        }

    }
}

我写了一个小扩展。

extension String {

    init(swiftLintMultiline strings: String...) {
        self = strings.reduce("", +)
    }
}

你可以这样使用它:

String(swiftLintMultiline:
    "Lorem ipsum dolor sit amet, consectetur adipiscing",
    "elit. Ut vulputate ultrices volutpat. Vivamus eget",
    "nunc maximus, tempus neque vel, suscipit velit.",
    "Quisque quam quam, malesuada et accumsan sodales,",
    "rutrum non odio. Praesent a est porta, hendrerit",
    "lectus scelerisque, pharetra magna. Proin id nulla",
    "pharetra, lobortis ipsum sit amet, vehicula elit. Nulla",
    "dapibus ipsum ipsum, sit amet congue arcu efficitur ac. Nunc imperdi"
)

Swift 4通过提供多行字符串文字支持解决了这个问题。要开始字符串字面量，添加三个双引号(" " " ")并按回车键，按回车键后开始写带有任何变量的字符串，换行符和双引号，就像你在记事本或任何文本编辑器中写的那样。要结束多行字符串文字再次写入(" " ")在新行。

参见下面的例子

     let multiLineStringLiteral = """
    This is one of the best feature add in Swift 4
    It let’s you write “Double Quotes” without any escaping
    and new lines without need of “\n”
    """

print(multiLineStringLiteral)

另一种方法是，如果你想使用带有预定义文本的字符串变量，

var textFieldData:String = "John"
myTextField.text = NSString(format: "Hello User, \n %@",textFieldData) as String
myTextField.numberOfLines = 0

我尝试了几种方法，但找到了一个更好的解决方案: 只需使用“文本视图”元素。它的文本自动显示多行! 找到这里:UITextField多行

正如litso所指出的，在一个表达式中重复使用+-操作符会导致Xcode Beta挂起(刚刚用Xcode 6 Beta 5检查过):Xcode 6 Beta无法编译

目前，多行字符串的另一种替代方法是使用一个字符串数组，并将其压缩为+:

var text = ["This is some text ",
            "over multiple lines"].reduce("", +)

或者，可以更简单地使用join:

var text = "".join(["This is some text ",
                    "over multiple lines"])