Xcode报错：Cannot infer contextual base in reference to member ‘utf8’

Xcode Playground中运行data(using:)方法发送报错。

let text = "Hello, Swift!"
if let binaryData = text.data(using: .utf8) {
    print(binaryData) // 打印二进制数据
}

报错内容为：

Cannot infer contextual base in reference to member 'utf8'
Value of type 'String' has no member 'data'

经排查发现，问题为缺少Foundation框架。

因为data(using:)方法属于Foundation框架，因此需要在文件的顶部引入Foundation框架：

import Foundation

重新运行后，问题得到解决。