Getting a KeyValuePair<> directly from a Dictionary<>

Question

I have System.Collections.Generic.Dictionary<A, B> dict where A and B are classes, and an instance A a (where dict.ContainsKey(a) is true).

Is it possible to get the KeyValuePair containing a directly from the Dictionary?
Or do I need to create a new KeyValuePair: new KeyValuePair<A, B>(a, dict[a])?

Answer 1

You need to create a new KeyValuePair¹ - but bear in mind that KVP is a value type (a struct) anyway, so it's not like you're introducing a new inefficiency by doing this. Any method returning a KVP would be creating a copy anyway - you're just creating the instance directly.

You could always add an extension method to IDictionary<TKey, TValue> if you wanted:

public static KeyValuePair<TKey, TValue> GetEntry
    (this IDictionary<TKey, TValue> dictionary,
     TKey key)
{
    return new KeyValuePair<TKey, TValue>(key, dictionary[key]);
}

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¹ I was aware that you could iterate over the dictionary entries and find the appropriate entry that way, but I can see no reason why you'd ever want to do so when you've got a perfectly good indexer which is O(1) instead of O(N).

Answer 2

As Dictionary<TKey, TValue> implements IEnumerable<KeyValuePair<TKey, TValue>>, you could use linq:

var pair = _dictionary.SingleOrDefault(p => p.Key == myKey);

Best Regards
Oliver Hanappi