LINQ の拡張メソッド群

EnumerableExtensions.cs

public static class LinqExtensions
{
	// KeySelector を指定して distinct
	public static IEnumerable<T> Distinct<T, TKey>(this IEnumerable<T> source, Func<T, TKey> keySelector)
	{
		IEnumerable<T> Enumerate()
		{
			var set = new HashSet<TKey>();
			foreach (var elem in source)
			{
				if (set.Add(keySelector(elem)))
				{
					yield return elem;
				}
			}
		}
		
		return source != null ? Enumerate() : throw new ArgumentNullException(nameof(source));
	}
    
    // TODO: Intersect, ...
}