/// <summary>
/// Converts an IDataProducer into a lookup.
/// </summary>
/// <param name="elementSelector">A transform function to produce a result element value from each element.</param>
/// <param name="keySelector">A function to extract a key from each element.</param>
/// <param name="keyComparer">Used to compare keys.</param>
/// <param name="source">The data source.</param>
/// <remarks>This will force all values to be buffered</remarks>
public static ILookup <TKey, TElement> ToLookup <TSource, TKey, TElement>(
this IDataProducer <TSource> source,
Func <TSource, TKey> keySelector, Func <TSource, TElement> elementSelector, IEqualityComparer <TKey> keyComparer)
{
source.ThrowIfNull("source");
keySelector.ThrowIfNull("keySelector");
elementSelector.ThrowIfNull("elementSelector");
keyComparer.ThrowIfNull("keyComparer");
EditableLookup <TKey, TElement> lookup = new EditableLookup <TKey, TElement>(keyComparer);
source.DataProduced += t => lookup.Add(keySelector(t), elementSelector(t));
source.EndOfData += () => lookup.TrimExcess();
return(lookup);
}