如果可能在声明类型的外部引用类型，则不要使用嵌套类型。

Do not use nested types if the type is likely to be referenced outside of the declaring type.

youdao

注意：当用引用返回值时永远不要使用括号，这样行不通。只能通过引用返回变量，而不是语句的结果。

Note: you should never use parentheses around your return variable when returning by reference, as this will not work.

youdao

注意：当用引用返回值时永远不要使用括号，这样行不通。只能通过引用返回变量，而不是语句的结果。

Note: you should never use parentheses around your return variable when returning by reference, as this will not work.

youdao