Create Extension Method TryGetValue(TKey, out TValue) of Enumerable<KeyValuePair<TKey, TValue>> just like of Dictionary<TKey, TValue>

Question

I have a Enumerable<KeyValuePair<TKey, TValue>> . I want to create a bool TryGetValue(TKey, out TValue) extension method of it just like it is available in Dictionary<TKey, TValue> .

I tried

public static bool TryGetValue<TKey, TValue>
(this Enumerable<KeyValuePair<TKey, TValue>> mapping, TKey key, out TValue value)
{
    bool retVal = false;

    KeyValuePair<TKey, TValue> kvp;

    kvp = mapping.First(x => x.Key.Equals(key));

    if(kvp.Key == null && kvp.Value == null)
    {
        retVal = false;
        value = default(TValue);
    }
    else
    {
        retVal = true;
        value = kvp.Value;
    }

    return retval;
}

Is this correct way? If not please suggest one.

Note:

I cannot use a Dictionary because Keys are repeated. Moreover it will only return the first matching value?

What happens to the rest?

We can leave them. I am sending KeyValuePair created from a DataTable. I am creating that DataTable using order by columnname in its query.

Answer 1

Why not just use a simple foreach loop?

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Example:

public static bool TryGetValue<TKey, TValue>
(this KeyValuePair<TKey, TValue>[] mapping, TKey key, out TValue value)
{
    foreach(var kvp in mapping)
        if (kvp.Key.Equals(key))
        {
            value = kvp.Value;
            return true;
        }

    value = default(TValue);
    return false;
}

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Your implementation will throw an exception if the key doesn't exists due to .First() , and FirstOrDefault() would be ugly since KeyValuePair is a struct and hence you can't just compare it to null .

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Sidenote:

Instead of extending KeyValuePair<TKey, TValue>[] , you probably want to use IEnumerable<KeyValuePair<TKey, TValue>> instead to be more flexible.