handle cases where count is 0 or negative

Author: Guiorgy

src/Enumerators/Split/SpanSplitStringSplitOptionsWithCountEnumerator.cs

@@ -33,15 +33,15 @@ public SpanSplitStringSplitOptionsWithCountEnumerator(ReadOnlySpan<char> source,
         {
             Span = source;
             Delimiter = delimiter;
-            CurrentCount = Math.Max(1, count);
+            CurrentCount = count.ThrowIfNegative();
 #if NET5_0_OR_GREATER
             TrimEntries = options.HasFlag(StringSplitOptions.TrimEntries);
 #else
             TrimEntries = false;
 #endif
             RemoveEmptyEntries = options.HasFlag(StringSplitOptions.RemoveEmptyEntries);
             CountExceedingBehaviour = countExceedingBehaviour.ThrowIfInvalid();
-            EnumerationDone = false;
+            EnumerationDone = count == 0;
             Current = default;
         }
 

src/Enumerators/Split/SpanSplitWithCountEnumerator.cs

@@ -31,9 +31,9 @@ public SpanSplitWithCountEnumerator(ReadOnlySpan<T> source, T delimiter, int cou
         {
             Span = source;
             Delimiter = delimiter;
-            CurrentCount = Math.Max(1, count);
+            CurrentCount = count.ThrowIfNegative();
             CountExceedingBehaviour = countExceedingBehaviour.ThrowIfInvalid();
-            EnumerationDone = false;
+            EnumerationDone = count == 0;
             Current = default;
         }
 

src/Enumerators/SplitAny/SpanSplitAnyStringSplitOptionsWithCountEnumerator.cs

@@ -33,15 +33,15 @@ public SpanSplitAnyStringSplitOptionsWithCountEnumerator(ReadOnlySpan<char> sour
         {
             Span = source;
             Delimiters = delimiters;
-            CurrentCount = Math.Max(1, count);
+            CurrentCount = count.ThrowIfNegative();
 #if NET5_0_OR_GREATER
             TrimEntries = options.HasFlag(StringSplitOptions.TrimEntries);
 #else
             TrimEntries = false;
 #endif
             RemoveEmptyEntries = options.HasFlag(StringSplitOptions.RemoveEmptyEntries);
             CountExceedingBehaviour = countExceedingBehaviour.ThrowIfInvalid();
-            EnumerationDone = false;
+            EnumerationDone = count == 0;
             Current = default;
         }
 

src/Enumerators/SplitAny/SpanSplitAnyWithCountEnumerator.cs

@@ -31,9 +31,9 @@ public SpanSplitAnyWithCountEnumerator(ReadOnlySpan<T> source, ReadOnlySpan<T> d
         {
             Span = source;
             Delimiters = delimiters;
-            CurrentCount = Math.Max(1, count);
+            CurrentCount = count.ThrowIfNegative();
             CountExceedingBehaviour = countExceedingBehaviour.ThrowIfInvalid();
-            EnumerationDone = false;
+            EnumerationDone = count == 0;
             Current = default;
         }
 

src/Enumerators/SplitSequence/SpanSplitSequenceStringSplitOptionsWithCountEnumerator.cs

@@ -34,15 +34,15 @@ public SpanSplitSequenceStringSplitOptionsWithCountEnumerator(ReadOnlySpan<char>
             Span = source;
             Delimiter = delimiter;
             DelimiterLength = delimiter.Length;
-            CurrentCount = Math.Max(1, count);
+            CurrentCount = count.ThrowIfNegative();
 #if NET5_0_OR_GREATER
             TrimEntries = options.HasFlag(StringSplitOptions.TrimEntries);
 #else
             TrimEntries = false;
 #endif
             RemoveEmptyEntries = options.HasFlag(StringSplitOptions.RemoveEmptyEntries);
             CountExceedingBehaviour = countExceedingBehaviour.ThrowIfInvalid();
-            EnumerationDone = false;
+            EnumerationDone = count == 0;
             Current = default;
         }
 

src/Enumerators/SplitSequence/SpanSplitSequenceWithCountEnumerator.cs

@@ -32,9 +32,9 @@ public SpanSplitSequenceWithCountEnumerator(ReadOnlySpan<T> source, ReadOnlySpan
             Span = source;
             Delimiter = delimiter;
             DelimiterLength = delimiter.Length;
-            CurrentCount = Math.Max(1, count);
+            CurrentCount = count.ThrowIfNegative();
             CountExceedingBehaviour = countExceedingBehaviour.ThrowIfInvalid();
-            EnumerationDone = false;
+            EnumerationDone = count == 0;
             Current = default;
         }
 

src/InternalExtensions.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Runtime.CompilerServices;
+
+namespace SpanExtensions
+{
+    static class InternalExtensions
+    {
+        /// <summary>
+        /// Throws an <see cref="ArgumentOutOfRangeException"/> if <paramref name="value"/> is negative.
+        /// </summary>
+        /// <param name="value">The argument to validate as non-negative.</param>
+        /// <param name="paramName">The name of the parameter with which <paramref name="value"/> corresponds.</param>
+        /// <returns><paramref name="value"/>.</returns>
+        public static int ThrowIfNegative(this int value
+#if NETCOREAPP3_0_OR_GREATER
+            , [CallerArgumentExpression(nameof(value))] string? paramName = null
+#endif
+            )
+        {
+#if NET8_0_OR_GREATER
+            ArgumentOutOfRangeException.ThrowIfNegative(value, paramName);
+#elif NETCOREAPP3_0_OR_GREATER
+            if(value < 0)
+            {
+                throw new ArgumentOutOfRangeException(paramName, value, $"{paramName} ('{value}') must be a non-negative value.");
+            }
+#else
+            if(value < 0)
+            {
+                throw new ArgumentOutOfRangeException(null, value, $" ('{value}') must be a non-negative value.");
+            }
+#endif
+
+            return value;
+        }
+    }
+}