使用 replacementOccurrences 以及 String.CompareOptions.regularExpresion 选项。

示例（Swift 3）：

Example (Swift 3):

var x = "<Hello, [play^ground+]>"
let y = x.replacingOccurrences(of: "[\\[\\]^+<>]", with: "7", options: .regularExpression, range: nil)
print(y)

输入要在方括号内替换的字符，如此[ \\字符]

Input characters which are to be replaced inside the square brackets like so [\\ Characters]

输出：

7Hello, 7play7ground777