像这样：

func removeSpecialCharsFromString(text: String) -> String {
    let okayChars : Set<Character> = 
        Set("abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLKMNOPQRSTUVWXYZ1234567890+-*=(),.:!_".characters)
    return String(text.characters.filter {okayChars.contains($0) })
}

以下是测试方法：

let s = removeSpecialCharsFromString("père") // "pre"