援引:
A class is immutable if each object of that class has a fixed value upon instantiation that cannot subsequently be changed.
原来可变不可变是mutate翻译过来的 哈哈哈
A class is immutable if each object of that class has a fixed value upon instantiation that cannot subsequently be changed.
原来可变不可变是mutate翻译过来的 哈哈哈