Reference return with possibility of invalid object

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I have a class of a B tree that has a search method, the search method must return a reference to the value associated with the search key, so the user can change it if he wants, this is a pair used in the tree:

template<class Key, class Value>
class Pair{
public:
Pair(){
    key = Key();
    value = Value();
}

Pair(Key key, Value value){
    this->key = key;
    this->value = value;
}

Key key;
Value value;
};

The problem is I don’t know what to do when the search finds nothing. So what I want is a method that can return a reference to something and somehow inform whether the value is valid or not, there are some ways to do this, I’ll list the ones I found and why I don’t want to use them:

  1. Fire an exception: I think it’s a very exaggerated action for a simple answer, and honestly I think it’s outside the scope of exceptions that should only report errors.
  2. Put an additional parameter that informs whether the value is valid or not: good and simple, but as I said I wanted a method with a single answer, I will equip this method if I do not find another.
  3. Use an additional structure that stores the reference and tells whether it is valid or not: I found this method interesting, the problem is that the object within the structure is a reference and should point somewhere even when the search does not return anything.

If you can tell me how to fix this I appreciate.

c++
  • 1

    Related or duplicate: http://answall.com/q/21767/101 or if not, maybe it is based on opinion.

  • Well connected, I don’t know if it’s duplicate but it’s almost, hehe, anyway thanks for the link, I’ll opt for the multiple returns. The question was based on multiple "opinions" but I came here in search of a definitive answer, so I listed the "opinions" that were possible, but I think I left open to new possibilities :s

  • I don’t think it’s a duplicate either, but I kind of agree with @bigown that it’s based on opinion. I would say that option 1 is easy to argue against in a concrete way, but options 2 and 3 are equally feasible and will depend essentially on what each one prefers. Particularly, I would choose the 3 because it does exactly as you wish: it indicates the failure of the result in a single place (in the class itself Pair). On the object need to "point somewhere", creates an empty reference, since it does not matter.

  • Actually, I don’t think there’s any unique and more recommended way to do this, I said I would use the second option but I will use the third (with a std::pair), because in the case of invalid reference the user can keep further away from it, just it check the pair.second to know whether or not to use the pair.first

1 answer

0

I can think of these two simple solutions.

template<typename K, typename V>
V *find(K key)
{
    ...
}
int *v = find(key);
if(v) ...

Or

template<typename K, typename V>
bool find(K key, V **value)
{
    ...
}

int *v;
if(find(10, &v)) ...

A better solution would be to create an iterator: http://www.cplusplus.com/reference/iterator/iterator/

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