Simplify StockMarket (C#) folder structure

83_Stock_Market/csharp/Extensions/ImmutableArrayExtensions.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Collections.Immutable;
+
+namespace Game.Extensions
+{
+    /// <summary>
+    /// Provides additional methods for the <see cref="ImmutableArray{T}"/> class.
+    /// </summary>
+    public static class ImmutableArrayExtensions
+    {
+        /// <summary>
+        /// Maps each element in an immutable array to a new value.
+        /// </summary>
+        /// <typeparam name="TSource">
+        /// The type of elements in the source array.
+        /// </typeparam>
+        /// <typeparam name="TResult">
+        /// The type of elements in the resulting array.
+        /// </typeparam>
+        /// <param name="source">
+        /// The source array.
+        /// </param>
+        /// <param name="selector">
+        /// Function which receives an element from the source array and its
+        /// index and returns the resulting element.
+        /// </param>
+        public static ImmutableArray<TResult> Map<TSource, TResult>(this ImmutableArray<TSource> source, Func<TSource, int, TResult> selector)
+        {
+            var builder = ImmutableArray.CreateBuilder<TResult>(source.Length);
+
+            for (var i = 0; i < source.Length; ++i)
+                builder.Add(selector(source[i], i));
+
+            return builder.MoveToImmutable();
+        }
+    }
+}