maui-linux/Xamarin.Forms.Core/EnumerableExtensions.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;

namespace Xamarin.Forms.Internals
{
	[EditorBrowsable(EditorBrowsableState.Never)]
	public static class EnumerableExtensions
	{

		public static IEnumerable<T> GetChildGesturesFor<T>(this IEnumerable<GestureElement> elements, Func<T, bool> predicate = null) where T : GestureRecognizer
		{
			if (elements == null)
				yield break;

			if (predicate == null)
				predicate = x => true;

			foreach (var element in elements)
				foreach (var item in element.GestureRecognizers)
				{
					var gesture = item as T;
					if (gesture != null && predicate(gesture))
						yield return gesture;
				}
		}

		public static IEnumerable<T> GetGesturesFor<T>(this IEnumerable<IGestureRecognizer> gestures, Func<T, bool> predicate = null) where T : GestureRecognizer
		{
			if (gestures == null)
				yield break;

			if (predicate == null)
				predicate = x => true;

			foreach (IGestureRecognizer item in new List<IGestureRecognizer>(gestures))
			{
				var gesture = item as T;
				if (gesture != null && predicate(gesture))
				{
					yield return gesture;
				}
			}
		}

		internal static IEnumerable<T> Append<T>(this IEnumerable<T> enumerable, T item)
		{
			foreach (T x in enumerable)
				yield return x;

			yield return item;
		}

		public static void ForEach<T>(this IEnumerable<T> enumeration, Action<T> action)
		{
			foreach (T item in enumeration)
			{
				action(item);
			}
		}

		public static IDictionary<TKey, List<TSource>> GroupToDictionary<TSource, TKey>(this IEnumerable<TSource> enumeration, Func<TSource, TKey> func)
		{
			var result = new Dictionary<TKey, List<TSource>>();
			foreach (TSource item in enumeration)
			{
				var group = func(item);
				if (!result.ContainsKey(group))
					result.Add(group, new List<TSource> { item });
				else
					result[group].Add(item);
			}
			return result;
		}

		public static int IndexOf<T>(this IEnumerable<T> enumerable, T item)
		{
			if (enumerable == null)
				throw new ArgumentNullException("enumerable");

			var i = 0;
			foreach (T element in enumerable)
			{
				if (Equals(element, item))
					return i;

				i++;
			}

			return -1;
		}

		public static int IndexOf<T>(this IEnumerable<T> enumerable, Func<T, bool> predicate)
		{
			var i = 0;
			foreach (T element in enumerable)
			{
				if (predicate(element))
					return i;

				i++;
			}

			return -1;
		}

		public static IEnumerable<T> Prepend<T>(this IEnumerable<T> enumerable, T item)
		{
			yield return item;

			foreach (T x in enumerable)
				yield return x;
		}
	}
}