Fixed and optimized split methods

src/CountExceedingBehaviour.cs

@@ -1,17 +1,78 @@
-namespace SpanExtensions
+using System;
+using System.Globalization;
+
+namespace SpanExtensions
 {
     /// <summary>
-    /// Defines the behaviour of a split operation when there are more split instances than there may be. 
-    /// </summary> 
+    /// Defines the behaviour of a split operation when there are more split instances than desired.
+    /// </summary>
     public enum CountExceedingBehaviour
     {
         /// <summary>
-        /// The last element returned will be all the remaining elements appended as one.
+        /// The last split returned will include all the remaining elements.
         /// </summary>
-        AppendLastElements,
+        AppendRemainingElements,
         /// <summary>
-        /// Every split instance more than permitted will not be returned. 
-        /// </summary> 
-        CutLastElements
+        /// Splits after the desired split count will be cut.
+        /// </summary>
+        CutRemainingElements
+    }
+
+    /// <summary>
+    /// Extension methods for <see cref="CountExceedingBehaviour"/>.
+    /// </summary>
+    static class CountExceedingBehaviourExtensions
+    {
+        static string? CountExceedingBehaviourInvalidFormat;
+
+        /// <summary>
+        /// Validates whether a specified value is a valid <see cref="CountExceedingBehaviour"/>.
+        /// </summary>
+        /// <param name="countExceedingBehaviour">The <see cref="CountExceedingBehaviour"/> to validate.</param>
+        /// <returns>The specified <see cref="CountExceedingBehaviour"/> if valid.</returns>
+        /// <exception cref="ArgumentException">If <paramref name="countExceedingBehaviour"/> is not valid.</exception>
+        public static CountExceedingBehaviour ThrowIfInvalid(this CountExceedingBehaviour countExceedingBehaviour)
+        {
+#if NET5_0_OR_GREATER
+            if(!Enum.IsDefined(countExceedingBehaviour))
+#else
+            if(!Enum.IsDefined(typeof(CountExceedingBehaviour), countExceedingBehaviour))
+#endif
+            {
+                if(CountExceedingBehaviourInvalidFormat == null)
+                {
+#if NET5_0_OR_GREATER
+                    string[] names = Enum.GetNames<CountExceedingBehaviour>();
+#else
+                    string[] names = Enum.GetNames(typeof(CountExceedingBehaviour));
+#endif
+                    CountExceedingBehaviourInvalidFormat = $"{nameof(CountExceedingBehaviour)} doesn't define an option with the value '{{0}}'. Valid values are {string.Join(", ", names)}.";
+                }
+
+                throw new ArgumentException(string.Format(CultureInfo.InvariantCulture, CountExceedingBehaviourInvalidFormat, (int)countExceedingBehaviour), nameof(countExceedingBehaviour));
+            }
+
+            return countExceedingBehaviour;
+        }
+
+        /// <summary>
+        /// Determines whether the current instance is <see cref="CountExceedingBehaviour.AppendRemainingElements"/>.
+        /// </summary>
+        /// <param name="countExceedingBehaviour">The <see cref="CountExceedingBehaviour"/> instance to test.</param>
+        /// <returns><see langword="true"/> if <paramref name="countExceedingBehaviour"/> is <see cref="CountExceedingBehaviour.AppendRemainingElements"/>; <see langword="false"/> otherwise.</returns>
+        public static bool IsAppendRemainingElements(this CountExceedingBehaviour countExceedingBehaviour)
+        {
+            return countExceedingBehaviour == CountExceedingBehaviour.AppendRemainingElements;
+        }
+
+        /// <summary>
+        /// Determines whether the current instance is <see cref="CountExceedingBehaviour.CutRemainingElements"/>.
+        /// </summary>
+        /// <param name="countExceedingBehaviour">The <see cref="CountExceedingBehaviour"/> instance to test.</param>
+        /// <returns><see langword="true"/> if <paramref name="countExceedingBehaviour"/> is <see cref="CountExceedingBehaviour.CutRemainingElements"/>; <see langword="false"/> otherwise.</returns>
+        public static bool IsCutRemainingElements(this CountExceedingBehaviour countExceedingBehaviour)
+        {
+            return countExceedingBehaviour == CountExceedingBehaviour.CutRemainingElements;
+        }
     }
-}
+}

src/Enumerators/Split/SpanSplitEnumerator.cs

@@ -10,7 +10,8 @@ namespace SpanExtensions.Enumerators
     {
         ReadOnlySpan<T> Span;
         readonly T Delimiter;
-        bool enumerationDone;
+        const int DelimiterLength = 1;
+        bool EnumerationDone;
 
         /// <summary>
         /// Gets the element in the collection at the current position of the enumerator.
@@ -26,8 +27,8 @@ public SpanSplitEnumerator(ReadOnlySpan<T> source, T delimiter)
         {
             Span = source;
             Delimiter = delimiter;
+            EnumerationDone = false;
             Current = default;
-            enumerationDone = false;
         }
 
         /// <summary>
@@ -44,22 +45,25 @@ public readonly SpanSplitEnumerator<T> GetEnumerator()
         /// <returns><see langword="true"/> if the enumerator was successfully advanced to the next element; <see langword="false"/> if the enumerator has passed the end of the collection.</returns>
         public bool MoveNext()
         {
-            if(enumerationDone)
+            if(EnumerationDone)
             {
                 return false;
             }
 
-            ReadOnlySpan<T> span = Span;
-            int index = span.IndexOf(Delimiter);
+            int delimiterIndex = Span.IndexOf(Delimiter);
 
-            if(index == -1 || index >= span.Length)
+            if(delimiterIndex == -1)
             {
-                enumerationDone = true;
-                Current = span;
+                EnumerationDone = true;
+
+                Current = Span;
+
                 return true;
             }
-            Current = span[..index];
-            Span = span[(index + 1)..];
+
+            Current = Span[..delimiterIndex];
+            Span = Span[(delimiterIndex + DelimiterLength)..];
+
             return true;
         }
     }

src/Enumerators/Split/SpanSplitStringSplitOptionsEnumerator.cs

@@ -9,8 +9,10 @@ public ref struct SpanSplitStringSplitOptionsEnumerator
     {
         ReadOnlySpan<char> Span;
         readonly char Delimiter;
-        readonly StringSplitOptions Options;
-        bool enumerationDone;
+        const int DelimiterLength = 1;
+        readonly bool TrimEntries;
+        readonly bool RemoveEmptyEntries;
+        bool EnumerationDone;
 
         /// <summary>
         /// Gets the element in the collection at the current position of the enumerator.
@@ -27,9 +29,10 @@ public SpanSplitStringSplitOptionsEnumerator(ReadOnlySpan<char> source, char del
         {
             Span = source;
             Delimiter = delimiter;
-            Options = options;
+            TrimEntries = options.ThrowIfInvalid().IsTrimEntriesSet();
+            RemoveEmptyEntries = options.IsRemoveEmptyEntriesSet();
+            EnumerationDone = false;
             Current = default;
-            enumerationDone = false;
         }
 
         /// <summary>
@@ -46,49 +49,44 @@ public readonly SpanSplitStringSplitOptionsEnumerator GetEnumerator()
         /// <returns><see langword="true"/> if the enumerator was successfully advanced to the next element; <see langword="false"/> if the enumerator has passed the end of the collection.</returns>
         public bool MoveNext()
         {
-            if(enumerationDone)
+            if(EnumerationDone)
             {
                 return false;
             }
 
-            ReadOnlySpan<char> span = Span;
-            int index = span.IndexOf(Delimiter);
-
-            if(index == -1 || index >= span.Length)
-            {
-                enumerationDone = true;
-                Current = span;
-                return true;
-            }
-            Current = span[..index];
-#if NET5_0_OR_GREATER
-            if(Options.HasFlag(StringSplitOptions.TrimEntries))
+            while(true) // if RemoveEmptyEntries options flag is set, repeat until a non-empty span is found, or the end is reached
             {
-                Current = Current.Trim();
-            }
-#endif
-            if(Options.HasFlag(StringSplitOptions.RemoveEmptyEntries))
-            {
-                if(Current.IsEmpty)
+                int delimiterIndex = Span.IndexOf(Delimiter);
+
+                if(delimiterIndex == -1)
                 {
-                    Span = span[(index + 1)..];
-                    if(Span.IsEmpty)
+                    EnumerationDone = true;
+
+                    Current = Span;
+
+                    if(TrimEntries)
                     {
-                        enumerationDone = true;
-                        return false;
+                        Current = Current.Trim();
                     }
-                    return MoveNext();
+
+                    return !(RemoveEmptyEntries && Current.IsEmpty);
                 }
 
-                Span = span[(index + 1)..];
-                if(Span.IsEmpty)
+                Current = Span[..delimiterIndex];
+                Span = Span[(delimiterIndex + DelimiterLength)..];
+
+                if(TrimEntries)
                 {
-                    enumerationDone = true;
+                    Current = Current.Trim();
                 }
+
+                if(RemoveEmptyEntries && Current.IsEmpty)
+                {
+                    continue;
+                }
+
                 return true;
             }
-            Span = span[(index + 1)..];
-            return true;
         }
     }
 }