Added enumerable support

Author: sakno

src/DotNext/Buffers/BufferWriterSlim.cs

@@ -353,6 +353,53 @@ public void Clear(bool reuseBuffer = false)
         position = 0;
     }
 
+    /// <summary>
+    /// Writes a collection of elements.
+    /// </summary>
+    /// <param name="collection">A collection of elements.</param>
+    /// <exception cref="ArgumentNullException"><paramref name="collection"/> is <see langword="null"/>.</exception>
+    public void Write(IEnumerable<T> collection)
+    {
+        ArgumentNullException.ThrowIfNull(collection);
+
+        switch (collection)
+        {
+            case List<T> list:
+                Write(CollectionsMarshal.AsSpan(list));
+                break;
+            case T[] array:
+                Write(new ReadOnlySpan<T>(array));
+                break;
+            case string str:
+                Write(Unsafe.BitCast<ReadOnlyMemory<char>, ReadOnlyMemory<T>>(str.AsMemory()).Span);
+                break;
+            case ArraySegment<T> segment:
+                Write(segment.AsSpan());
+                break;
+            default:
+                WriteSlow(collection);
+                break;
+        }
+    }
+
+    private void WriteSlow(IEnumerable<T> collection)
+    {
+        using var enumerator = collection.GetEnumerator();
+        if (collection.TryGetNonEnumeratedCount(out var count))
+        {
+            var buffer = InternalGetSpan(count);
+            for (var i = 0; i < buffer.Length && enumerator.MoveNext(); i++)
+            {
+                buffer[i] = enumerator.Current;
+            }
+        }
+
+        while (enumerator.MoveNext())
+        {
+            Add(enumerator.Current);
+        }
+    }
+
     /// <summary>
     /// Releases internal buffer used by this builder.
     /// </summary>