[Array] add count field.

Author: reegeek

src/StructLinq/Array/ArrayEnumerable.cs

@@ -9,24 +9,27 @@ public struct ArrayEnumerable<T> : IStructCollection<T, ArrayStructEnumerator<T>
         private readonly T[] array;
         private int length;
         private int start;
+        private int count;
         #endregion
+
         public ArrayEnumerable(T[] array, int start, int length)
         {
             this.array = array;
             this.length = length;
             this.start = start;
+            count = length - start;
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public readonly ArrayStructEnumerator<T> GetEnumerator()
         {
-            return new ArrayStructEnumerator<T>(array, start, Count);
+            return new ArrayStructEnumerator<T>(array, start, count);
         }
 
         public readonly int Count
         {
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            get => MathHelpers.Max(0, length - start);
+            get => count;
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -36,7 +39,10 @@ public void Slice(uint start, uint? length)
             {
                 this.start = (int)start + this.start;
                 if (length.HasValue)
+                {
                     this.length = MathHelpers.Min((int)length.Value + this.start, this.length);
+                    count = MathHelpers.Max(0, this.length - this.start);
+                }
             }
         }