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What is the ?-->? operator in C++?
There is no such operator in C++. Sometimes, we need to create wrapper types. For example, types like unique_ptr, shared_ptr, optional and similar. Usually, these types have an accessor member function called .get but they also provide the operator→ to support direct access to the contained value similarly to what ordinary pointers do.
The problem is that sometimes we have a few of these types nested into each other. This means that we need to call .get multiple times or to have a lot of dereference operators until we reach the value.
Something like this −
wrapper<wrapper<std::string>> wp; wp.get().get().length(); wp.get()->length();
This can be a bit ugly. If we can replace one .get() with an arrow, it would be nice if we could replace the second .get() as well. For this, the C++98 introduced a long arrow operator.
wrapper<wrapper<std::string>> wp; wp--->length();
What if we have another layer of wrapping? Just make a longer arrow.
wrapper<wrapper<wrapper<std::string>>> wp; wp----->length();
The long arrow is not a single operator, but a combination of multiple operators. In this case, a normal -> operator and the postfix decrement operator --.
So, when we write wp----→length(), the compiler sees ((wp--)--)→length().
If we define the postfix -- to be the same as the dereference operator, we get the long arrow, and the even longer arrow operators −
template <typename T>
class wrapper {
public:
T* operator->() { return &t; }
T& operator--(int) { return t; }
private:
T t;
};
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