c++ - 不明白return *this "as a whole"的用法

Question

我无法弄清楚我正在阅读的书中的以下部分实际上做了什么。

//this function supposed to mimic the += operator
Sales_data& Sales_data::combine(const Sales_data &rhs)
{
    units_sold += rhs.units_sold; // add the members of rhs into
    revenue += rhs.revenue;  // the members of ''this'' object
    return *this; // return the object on which the function was called
}

int main()
{
    //...sth sth

    Sales_data total, trans; 
    //assuming both total and trans were also defined...
    total.combine(trans);
    //and here the book says:
    //we do need to use this to access the object as a whole.
    //Here the return statement dereferences this to obtain the object on which the
    //function is executing. That is, for the call above, we return a reference to total.
    //*** what does it mean "we return a reference to total" !?
}

我应该说我以前对 C# 有一点了解，并不真正理解 return *this; 究竟如何影响 total object。

Answer 1

琐事

该函数正在返回对与其自身相同的类型的引用，并且它返回...自身。

指针类型

因为返回类型是引用类型(Sales_data&)，而this是一个指针类型( Sales_data* )，你必须取消引用它，因此 *this ，它实际上是对我们调用其成员函数的对象的引用。

用法

它真正允许的是方法链。

Sales_data total;
Sales_data a, b, c, d;

total.combine(a).combine(b).combine(c).combine(d);

有时是竖写的:

total
    .combine(a)
    .combine(b)
    .combine(c)
    .combine(d);

我敢肯定你已经看到了:

cout << "Hello" << ' ' << "World!" << endl;

在上面的例子中，重载了operator<<返回对输出流的引用。