如果变量是函数参数，则使用函数填充字符串变量不起作用

void fillStringVariable(std::string& str) {
    str = "Filled";
}

std::string variable = "Empty";
fillStringVariable(variable);
// variable现在的值为"Filled"

void fillStringVariable(StringBuilder str) {
    str.append("Filled");
}

StringBuilder variable = new StringBuilder("Empty");
fillStringVariable(variable);
// variable现在的值为"Filled"

def fill_string_variable(str_list):
    str_list[0] = "Filled"

variable = ["Empty"]
fill_string_variable(variable)
# variable现在的值为["Filled"]