feat: add IList<T>.Rotate and Span<T>.Rotate

Author: oliverbooth

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## 5.0.0 - [Unreleased]
 
+### Added
+
+- X1OD: Added `IList<T>.Rotate(int)`.
+- X1OD: Added `Span<T>.Rotate(int)`.
+
 ### Changed
 
 - X10D: Removed `IEnumerable<T>.GreatestCommonFactor` for all integer types in favour of generic math.

X10D.Tests/src/Collections/ListTests.cs

@@ -211,6 +211,46 @@ public void RemoveRange_ShouldRemoveElements_GivenList()
         Assert.That(list, Is.EqualTo(new[] { 1, 2, 7, 8, 9, 10 }).AsCollection);
     }
 
+    [Test]
+    public void Rotate_ShouldShiftElements_ByNegativeShiftAmount()
+    {
+        int[] array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+        int[] expected = [5, 6, 7, 8, 9, 10, 1, 2, 3, 4];
+
+        array.Rotate(-4);
+
+        Assert.That(array, Is.EqualTo(expected).AsCollection);
+    }
+
+    [Test]
+    public void Rotate_ShouldShiftElements_ByPositiveShiftAmount()
+    {
+        int[] array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+        int[] expected = [7, 8, 9, 10, 1, 2, 3, 4, 5, 6];
+
+        array.Rotate(4);
+
+        Assert.That(array, Is.EqualTo(expected).AsCollection);
+    }
+
+    [Test]
+    public void Rotate_ShouldNotShiftElements_WithShift0()
+    {
+        int[] array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+        int[] expected = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+        array.Rotate(0);
+
+        Assert.That(array, Is.EqualTo(expected).AsCollection);
+    }
+
+    [Test]
+    public void Rotate_ShouldThrowArgumentNullException_GivenNullSource()
+    {
+        int[] array = null!;
+        Assert.Throws<ArgumentNullException>(() => array.Rotate(0));
+    }
+
     [Test]
     public void Shuffle_ShouldReorder_GivenNotNull()
     {

X10D.Tests/src/Collections/SpanTest.cs

@@ -1,4 +1,5 @@
 using NUnit.Framework;
+using X10D.Collections;
 #if !NET9_0_OR_GREATER
 using X10D.Collections;
 #endif
@@ -32,6 +33,39 @@ public void Replace_ShouldDoNothing_GivenSpanWithNoMatchingElements()
         Assert.That(span.ToArray(), Is.EqualTo(new[] { 1, 2, 3, 2, 5, 2, 7, 2, 9, 2, 11, 2, 13, 2, 15, 2 }));
     }
 
+    [Test]
+    public void Rotate_ShouldShiftElements_ByNegativeShiftAmount()
+    {
+        Span<int> array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+        Span<int> expected = [5, 6, 7, 8, 9, 10, 1, 2, 3, 4];
+
+        array.Rotate(-4);
+
+        Assert.That(array.ToArray(), Is.EqualTo(expected.ToArray()).AsCollection);
+    }
+
+    [Test]
+    public void Rotate_ShouldShiftElements_ByPositiveShiftAmount()
+    {
+        Span<int> array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+        Span<int> expected = [7, 8, 9, 10, 1, 2, 3, 4, 5, 6];
+
+        array.Rotate(4);
+
+        Assert.That(array.ToArray(), Is.EqualTo(expected.ToArray()).AsCollection);
+    }
+
+    [Test]
+    public void Rotate_ShouldNotShiftElements_WithShift0()
+    {
+        Span<int> array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+        Span<int> expected = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+        array.Rotate(0);
+
+        Assert.That(array.ToArray(), Is.EqualTo(expected.ToArray()).AsCollection);
+    }
+
 #if !NET9_0_OR_GREATER
     [Test]
     public void Split_OnEmptySpan_ShouldYieldNothing_UsingCharDelimiter_GivenReadOnlySpan()

X10D/src/Collections/ListExtensions.cs

@@ -1,5 +1,6 @@
 using System.Diagnostics.Contracts;
 using X10D.Core;
+using X10D.Math;
 
 #pragma warning disable CA5394
 
@@ -249,6 +250,42 @@ public static void RemoveRange<T>(this IList<T> source, Range range)
         }
     }
 
+    /// <summary>
+    ///     Shifts the elements of the current list by a specified amount, wrapping them in the process.
+    /// </summary>
+    /// <param name="source">The list of elements to shift.</param>
+    /// <param name="shift">The amount to shift.</param>
+    /// <typeparam name="T">The type of the elements in <paramref name="source" />.</typeparam>
+    /// <exception cref="ArgumentNullException"><paramref name="source" /> is <see langword="null" />.</exception>
+    public static void Rotate<T>(this IList<T> source, int shift)
+    {
+        if (source is null)
+        {
+            throw new ArgumentNullException(nameof(source));
+        }
+
+        if (shift == 0)
+        {
+            return;
+        }
+
+        shift = shift.Mod(source.Count);
+        Reverse(source, 0, source.Count - 1);
+        Reverse(source, 0, shift - 1);
+        Reverse(source, shift, source.Count - 1);
+        return;
+
+        static void Reverse(IList<T> list, int start, int end)
+        {
+            while (start < end)
+            {
+                (list[start], list[end]) = (list[end], list[start]);
+                start++;
+                end--;
+            }
+        }
+    }
+
     /// <summary>
     ///     Reorganizes the elements in a list by implementing a Fisher-Yates shuffle.
     /// </summary>

X10D/src/Collections/SpanExtensions.cs

@@ -1,3 +1,5 @@
+using X10D.Math;
+
 namespace X10D.Collections;
 
 /// <summary>
@@ -16,6 +18,37 @@ public static ReadOnlySpan<T> AsReadOnly<T>(this in Span<T> source)
         return source;
     }
 
+    /// <summary>
+    ///     Shifts the elements of the current span by a specified amount, wrapping them in the process.
+    /// </summary>
+    /// <param name="source">The span of elements to shift.</param>
+    /// <param name="shift">The amount to shift.</param>
+    /// <typeparam name="T">The type of the elements in <paramref name="source" />.</typeparam>
+    /// <exception cref="ArgumentNullException"><paramref name="source" /> is <see langword="null" />.</exception>
+    public static void Rotate<T>(this Span<T> source, int shift)
+    {
+        if (shift == 0)
+        {
+            return;
+        }
+
+        shift = shift.Mod(source.Length);
+        Reverse(source, 0, source.Length - 1);
+        Reverse(source, 0, shift - 1);
+        Reverse(source, shift, source.Length - 1);
+        return;
+
+        static void Reverse(Span<T> span, int start, int end)
+        {
+            while (start < end)
+            {
+                (span[start], span[end]) = (span[end], span[start]);
+                start++;
+                end--;
+            }
+        }
+    }
+
 #if !NET9_0_OR_GREATER
     /// <summary>
     ///     Splits a span of elements into sub-spans based on a delimiting element.