rename to SplitEnumerator and fix test

MediaBrowser.Common/Extensions/SplitStringExtensions.cs

@@ -0,0 +1,102 @@
+/*
+MIT License
+
+Copyright (c) 2019 Gérald Barré
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+ */
+#nullable enable
+#pragma warning disable CS1591
+#pragma warning disable CA1034
+using System;
+using System.Diagnostics.Contracts;
+using System.Runtime.InteropServices;
+
+namespace MediaBrowser.Common.Extensions
+{
+    /// <summary>
+    /// Extension class for splitting lines without unnecessary allocations.
+    /// </summary>
+    public static class SplitStringExtensions
+    {
+        /// <summary>
+        /// Creates a new string split enumerator.
+        /// </summary>
+        /// <param name="str">The string to split.</param>
+        /// <param name="separator">The separator to split on.</param>
+        /// <returns>The enumerator struct.</returns>
+        [Pure]
+        public static SplitEnumerator SpanSplit(this string str, char separator) => new (str.AsSpan(), separator);
+
+        /// <summary>
+        /// Creates a new span split enumerator.
+        /// </summary>
+        /// <param name="str">The span to split.</param>
+        /// <param name="separator">The separator to split on.</param>
+        /// <returns>The enumerator struct.</returns>
+        [Pure]
+        public static SplitEnumerator Split(this ReadOnlySpan<char> str, char separator) => new (str, separator);
+
+        [StructLayout(LayoutKind.Auto)]
+        public ref struct SplitEnumerator
+        {
+            private readonly char _separator;
+            private ReadOnlySpan<char> _str;
+
+            public SplitEnumerator(ReadOnlySpan<char> str, char separator)
+            {
+                _str = str;
+                _separator = separator;
+                Current = default;
+            }
+
+            public ReadOnlySpan<char> Current { get; private set; }
+
+            public readonly SplitEnumerator GetEnumerator() => this;
+
+            public bool MoveNext()
+            {
+                if (_str.Length == 0)
+                {
+                    return false;
+                }
+
+                var span = _str;
+                var index = span.IndexOf(_separator);
+                if (index == -1)
+                {
+                    _str = ReadOnlySpan<char>.Empty;
+                    Current = span;
+                    return true;
+                }
+
+                if (index < span.Length - 1 && span[index] == _separator)
+                {
+                    Current = span.Slice(0, index);
+                    _str = span[(index + 1)..];
+                    return true;
+                }
+
+                Current = span.Slice(0, index);
+                _str = span[(index + 1)..];
+                return true;
+            }
+        }
+    }
+}