Re: "One"-to-one associations and equality operators
Am 27.11.2011 13:59, schrieb kelvSYC:
I'm having a conundrum: it seems I can't reconcile equality operators
and (pseudo) one-to-one associations. Suppose we have two classes,
Key and Value, like so:
struct Key {
bool operator==(const Key& key) const;
const Value& getValue() const;
};
struct Value {
boost::weak_ptr<Key> key;
};
So each Value is tied to one (specific) Key among those that are
equal. The challenge is: how do I make a central Key-Value repository
using C++03, such that every Value in the repository is linked to its
Key? std::map<Key, Value> doesn't work (I don't think, since I think
the Key would be copied, and thus the Value loses its association with
the Key).
You only mention ==, which is not used by std::map and would not induce a strictly weak ordering (at least one that is reasonably written ;-)). In the following I assume that your problem exists for your operator< or the actual ordering criterion used or that you will use boost's unordered containers.
Would std::map<boost::shared_ptr<Key>,
boost::shared_ptr<Value>> do the trick? Is there an easier solution?
If I understand you correctly, your criterion depends on identities of keys, not of their values. Most smart pointers, like boost::shared_ptr, will satisfy this. But any other identity wrapper will do so as well. In theory you could use boost::reference_wrapper, for example. But this means that you need to take care for the life-cycle management of the referenced keys "manually". If you can ensure that the keys have a life-time that is not shorter than that of the container, there should be no problem with using something like boost::reference_wrapper.
HTH & Greetings from Bremen,
Daniel Kr?gler
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