<PackageReference Include="NETStandard.Library" Version="2.0.3" />

System.Collections.ObjectModel.Collection<T>

namespace System.Collections.ObjectModel { public class Collection<T> : ICollection<T>, IEnumerable<T>, IEnumerable, IList<T>, IReadOnlyCollection<T>, IReadOnlyList<T>, ICollection, IList { public int Count { get; } public T this[int index] { get; set; } protected IList<T> Items { get; } object IList.this[int index] { get; set; } public Collection(); public Collection(IList<T> list); public void Add(T item); public void Clear(); protected virtual void ClearItems(); public bool Contains(T item); public void CopyTo(T[] array, int index); public IEnumerator<T> GetEnumerator(); public int IndexOf(T item); public void Insert(int index, T item); protected virtual void InsertItem(int index, T item); public bool Remove(T item); public void RemoveAt(int index); protected virtual void RemoveItem(int index); protected virtual void SetItem(int index, T item); } }