无法使点'.'超载. C ++中的运算符 [英] Inability to overload Dot '.' operator in c++

问题描述

我很难理解Stroustrup的解释，即如果运算符重载."，则必须面对什么困难.被允许.

I have hard time understanding the explanation from Stroustrup for what difficulties one must have faced, if operator overloading for '.' was allowed.

请参阅Bjarne Stroustrup的这句话:

See this quote from Bjarne Stroustrup:

操作员. (点)原则上可以使用与->相同的技术来重载.但是，这样做可能会引起有关操作是否用于对象重载的问题.或所指的对象.例如:

Operator . (dot) could in principle be overloaded using the same technique as used for ->. However, doing so can lead to questions about whether an operation is meant for the object overloading . or an object referred to by . For example:

class Y {
public:
    void f();
    // ...
};

class X {    // assume that you can overload .
    Y* p;
    Y& operator.() { return *p; }
    void f();
    // ...
};

void g(X& x)
{
    x.f();    // X::f or Y::f or error?
}

在上面的示例中，为什么在执行x.f()时会有任何困惑?

In the above example why should there be any confusion while executing x.f() ?

Y& operator.() { return *p; }

这是我的想法:

1. operator.()在x上被调用，因此Y& operator.()( return *p; }应该被调用不是很明显和直观吗?
2. 在返回指向类型为Y的对象的*p之后，应最终调用Y::f()(不是X::f())

1. operator.() is called on x hence isn't it obvious and intuitive that Y& operator.()( return *p; } should be called ?
2. Upon returning *p which points to object of type Y and hence Y::f() should be called finally ( not X::f() )

我在Stroustup的解释中缺少什么?为什么不是那么简单?

What am i missing in Stroustup's explanation? Why is it not straightforward?

推荐答案

已经取得了一些进展: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4477.pdf .由于某些技术问题，它将不在C ++ 17中使用，但我希望在C ++ 20中能够看到它.

There has been some progress: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4477.pdf . Due to some technical problems this won't be in C++17, but I hope to see it for C++20.

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