ILSpy/ICSharpCode.Decompiler/Util/EmptyList.cs

// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
#nullable enable

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

namespace ICSharpCode.Decompiler.Util
{
	[Serializable]
	public sealed class EmptyList<T> : IList<T>, IEnumerator<T>, IReadOnlyList<T>
	{
		public static readonly EmptyList<T> Instance = new EmptyList<T>();

		private EmptyList() { }

		public T this[int index] {
			get { throw new ArgumentOutOfRangeException(nameof(index)); }
			set { throw new ArgumentOutOfRangeException(nameof(index)); }
		}

		public int Count {
			get { return 0; }
		}

		bool ICollection<T>.IsReadOnly {
			get { return true; }
		}

		int IList<T>.IndexOf(T item)
		{
			return -1;
		}

		void IList<T>.Insert(int index, T item)
		{
			throw new NotSupportedException();
		}

		void IList<T>.RemoveAt(int index)
		{
			throw new NotSupportedException();
		}

		void ICollection<T>.Add(T item)
		{
			throw new NotSupportedException();
		}

		void ICollection<T>.Clear()
		{
		}

		bool ICollection<T>.Contains(T item)
		{
			return false;
		}

		void ICollection<T>.CopyTo(T[] array, int arrayIndex)
		{
		}

		bool ICollection<T>.Remove(T item)
		{
			return false;
		}

		IEnumerator<T> IEnumerable<T>.GetEnumerator()
		{
			return this;
		}

		System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
		{
			return this;
		}

		T IEnumerator<T>.Current {
			get { throw new NotSupportedException(); }
		}

		object IEnumerator.Current {
			get { throw new NotSupportedException(); }
		}

		void IDisposable.Dispose()
		{
		}

		bool IEnumerator.MoveNext()
		{
			return false;
		}

		void IEnumerator.Reset()
		{
		}
	}

	public static class Empty<T>
	{
		public static readonly T[] Array = System.Array.Empty<T>();
	}

	public struct Unit { }
}