Re: Any dot-operator proposals out there?

From:
"Patrik Kahari" <patrik.kahari@googlemail.com>
Newsgroups:
comp.std.c++
Date:
Tue, 20 Feb 2007 14:54:20 CST
Message-ID:
<1171992689.399737.96340@q2g2000cwa.googlegroups.com>

I've occasionally wanted to be able to override the dot-operator [...]
My search for a proposal to add support for this operator has been without success,
however, and I wonder why.


Yes, In "the design and evolution of c++" Bjarne Stroustrup describes
why he did not allow it.
If i remeber correctly the resoning goes something like this;

The biggest need for a dot operator would probably be the
implementation of wrapper objects that would behave just like the
object it wrapped. As in the dot operator would return a reference to
the underlying wrapped object and not to the wrapper itself. But then
there would be no way for a client to access any methods or data of
the wrapped object itself. We can just overload the -> operator
instead and avoid the problem.

An example:

<CODE>

#include <iostream>

template <typename T>
struct Wrapper {
    Wrapper(T t):t_(t), count(0) {}

    T* operator->() {
        ++count;
        return &t_;
    }

/*
    T& operator.() {
        ++count;
        return t_;
    }
*/

    size_t count;
    T t_;
};

inline void test () {
    std::string s("test");
    Wrapper<std::string> ws(s);
    int length = ws->length();
    int count = ws.count;
/* if we had overloaded the '.' operator instead of the '->' operator,
we would have no way to get access to the 'count' member */
}

</CODE>

Regards Patrik

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