Daily update 2 on 20240228 by nitload youmu

StgSharp.Common/Collections/ListSegment.cs

@@ -0,0 +1,90 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+using System.Xml.Serialization;
+
+namespace StgSharp.Collections
+{
+    /// <summary>
+    /// Part of a collection. This contains a direct reference to origin collection,
+    /// so all change to origin collection will be reflected in this object.
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    public struct ListSegment<T> : ICollection<T>
+    {
+        private List<T> _collection;
+        private int _begin;
+        private int _length;
+
+
+        public ListSegment(List<T> collection, int begin, int length)
+        {
+            ArgumentNullException.ThrowIfNull(collection);
+            ArgumentOutOfRangeException.ThrowIfLessThan(begin, 0);
+            ArgumentOutOfRangeException.ThrowIfLessThan(length, 0);
+            ArgumentOutOfRangeException.ThrowIfLessThan(begin + length, collection.Count);
+            _collection = collection;
+            _begin = begin;
+            _length = length;
+        }   
+
+        public int Count => _length;
+
+        public bool IsReadOnly => true;
+
+        public T this[int indexValue]
+        {
+            get {
+                ArgumentOutOfRangeException.ThrowIfLessThan(indexValue, 0);
+                ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual(indexValue, _length);
+                return _collection[indexValue + _begin];
+            }
+        }
+
+        void ICollection<T>.Add(T item)
+        {
+            throw new NotSupportedException();
+        }
+
+        void ICollection<T>.Clear()
+        {
+            throw new NotSupportedException();
+        }
+
+        public bool Contains(T item)
+        {
+            var index=  _collection.IndexOf(item);
+            return index >= _begin && index < _length + index;
+        }
+
+        public void CopyTo(T[] array, int arrayIndex)
+        {
+            ArgumentNullException.ThrowIfNull(array);
+            var span = CollectionsMarshal.AsSpan<T>(_collection).Slice(_begin, _length);
+            var target = new Span<T>(array, arrayIndex,_length);
+            span.CopyTo(target);
+        }
+
+        public IEnumerator<T> GetEnumerator()
+        {
+            for (int i = _begin; i < _length; i++)
+            {
+                yield return this[i];
+            }
+        }
+
+        bool ICollection<T>.Remove(T item)
+        {
+            throw new NotSupportedException();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+    }
+}