从有很多标点的 String 中取出所有单词

var str = "Hello, playground. Have a nice day!"

extension String {
    
    var words: [String] {
        return components(separatedBy: .punctuationCharacters)
        .joined()
        .components(separatedBy: .whitespaces)
        .filter({ !$0.isEmpty })
    }
    
}

print(str.words)