Move additional methods into child namespaces (#7)

X10D.Tests/src/Collections/ArrayTests.cs

@@ -0,0 +1,106 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Collections;
+using X10D.Core;
+
+namespace X10D.Tests.Collections;
+
+[TestClass]
+public class ArrayTests
+{
+    [TestMethod]
+    [DataRow(1)]
+    [DataRow("f")]
+    [DataRow(true)]
+    public void AsArrayShouldGiveLength1(object o)
+    {
+        object[] array = o.AsArray()!;
+        Assert.IsNotNull(array);
+        Assert.IsTrue(array.Length == 1);
+    }
+
+    [TestMethod]
+    [DataRow(1)]
+    [DataRow("f")]
+    [DataRow(true)]
+    public void AsArrayShouldContainObject(object o)
+    {
+        object[] array = o.AsArray()!;
+        Assert.IsNotNull(array);
+        Assert.AreEqual(o, array[0]);
+    }
+
+    [TestMethod]
+    public void AsReadOnlyShouldBeReadOnly()
+    {
+        var array = new object[] {1, "f", true};
+        var readOnly = array.AsReadOnly();
+        Assert.IsNotNull(readOnly);
+        Assert.IsTrue(readOnly.Count == 3);
+
+        // ReSharper disable once ConvertTypeCheckToNullCheck
+        Assert.IsTrue(readOnly is IReadOnlyCollection<object>);
+    }
+
+    [TestMethod]
+    public void AsReadOnlyNullShouldThrow()
+    {
+        object[]? array = null;
+        Assert.ThrowsException<ArgumentNullException>(array!.AsReadOnly);
+    }
+
+    [TestMethod]
+    [DataRow]
+    [DataRow(1)]
+    [DataRow(1, 2, 3)]
+    [DataRow(1, 2, 3, 4, 5)]
+    public void ClearShouldFillDefault(params int[] args)
+    {
+        args.Clear();
+
+        int[] clearedArray = Enumerable.Repeat(0, args.Length).ToArray();
+        CollectionAssert.AreEqual(clearedArray, args);
+    }
+
+    [TestMethod]
+    public void ClearNullShouldThrow()
+    {
+        int[]? array = null;
+        Assert.ThrowsException<ArgumentNullException>(array!.Clear);
+        Assert.ThrowsException<ArgumentNullException>(() => array!.Clear(0, 0));
+    }
+
+    [TestMethod]
+    [DataRow]
+    [DataRow(1)]
+    [DataRow(1, 2, 3)]
+    [DataRow(1, 2, 3, 4, 5)]
+    public void FillShouldBeCorrect(params int[] args)
+    {
+        args.Fill(1);
+
+        int[] comparison = Enumerable.Repeat(1, args.Length).ToArray();
+        CollectionAssert.AreEqual(comparison, args);
+    }
+
+    [TestMethod]
+    public void FillNullShouldThrow()
+    {
+        int[]? array = null;
+        Assert.ThrowsException<ArgumentNullException>(() => array!.Fill(0));
+        Assert.ThrowsException<ArgumentNullException>(() => array!.Fill(0, 0, 0));
+    }
+
+    [TestMethod]
+    [DataRow(1)]
+    [DataRow(1, 2, 3)]
+    [DataRow(1, 2, 3, 4, 5)]
+    public void FillSlicedShouldBeCorrect(params int[] args)
+    {
+        int first = args[0];
+        args.Fill(1, 1, args.Length - 1);
+
+        int[] comparison = Enumerable.Repeat(1, args.Length - 1).ToArray();
+        Assert.AreEqual(first, args[0]);
+        CollectionAssert.AreEqual(comparison, args[1..]);
+    }
+}

X10D.Tests/src/Core/ArrayTests.cs

@@ -1,60 +0,0 @@
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using X10D.Core;
-
-namespace X10D.Tests.Core;
-
-[TestClass]
-public class ArrayTests
-{
-    [TestMethod]
-    [DataRow(1)]
-    [DataRow("f")]
-    [DataRow(true)]
-    public void AsArray(object o)
-    {
-        object[] array = o.AsArray();
-        Assert.IsNotNull(array);
-        Assert.IsTrue(array.Length == 1);
-        Assert.AreEqual(o, array[0]);
-    }
-
-    [TestMethod]
-    [DataRow]
-    [DataRow(1)]
-    [DataRow(1, 2, 3)]
-    [DataRow(1, 2, 3, 4, 5)]
-    public void Clear(params int[] args)
-    {
-        args.Clear();
-
-        int[] comparison = Enumerable.Repeat(0, args.Length).ToArray();
-        CollectionAssert.AreEqual(args, comparison);
-    }
-
-    [TestMethod]
-    public void ClearNull()
-    {
-        int[]? array = null;
-        Assert.ThrowsException<ArgumentNullException>(array!.Clear);
-    }
-
-    [TestMethod]
-    [DataRow]
-    [DataRow(1)]
-    [DataRow(1, 2, 3)]
-    [DataRow(1, 2, 3, 4, 5)]
-    public void Fill(params int[] args)
-    {
-        args.Fill(1);
-
-        int[] comparison = Enumerable.Repeat(1, args.Length).ToArray();
-        CollectionAssert.AreEqual(args, comparison);
-    }
-
-    [TestMethod]
-    public void FillNull()
-    {
-        int[]? array = null;
-        Assert.ThrowsException<ArgumentNullException>(() => array!.Fill(0));
-    }
-}

X10D.Tests/src/Core/CoreTests.cs

@@ -1,6 +1,5 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using X10D.Core;
-using X10D.Text;
 
 namespace X10D.Tests.Core;
 

X10D.Tests/src/Core/StringTests.cs

@@ -8,50 +8,6 @@ namespace X10D.Tests.Core;
 [TestClass]
 public class StringTests
 {
-    /// <summary>
-    ///     Tests <see cref="StringExtensions.AsNullIfEmpty" />.
-    /// </summary>
-    [TestMethod]
-    public void AsNullIfEmpty()
-    {
-        const string sampleString = "Hello World";
-        const string whitespaceString = " ";
-        const string emptyString = "";
-        const string? nullString = null;
-
-        string sampleResult = sampleString.AsNullIfEmpty();
-        string whitespaceResult = whitespaceString.AsNullIfEmpty();
-        string emptyResult = emptyString.AsNullIfEmpty();
-        string? nullResult = nullString.AsNullIfEmpty();
-
-        Assert.AreEqual(sampleString, sampleResult);
-        Assert.AreEqual(whitespaceString, whitespaceResult);
-        Assert.AreEqual(nullString, emptyResult);
-        Assert.AreEqual(nullString, nullResult);
-    }
-
-    /// <summary>
-    ///     Tests <see cref="StringExtensions.AsNullIfWhiteSpace" />.
-    /// </summary>
-    [TestMethod]
-    public void AsNullIfWhiteSpace()
-    {
-        const string sampleString = "Hello World";
-        const string whitespaceString = " ";
-        const string emptyString = "";
-        const string? nullString = null;
-
-        string sampleResult = sampleString.AsNullIfWhiteSpace();
-        string whitespaceResult = whitespaceString.AsNullIfWhiteSpace();
-        string emptyResult = emptyString.AsNullIfWhiteSpace();
-        string? nullResult = nullString.AsNullIfWhiteSpace();
-
-        Assert.AreEqual(sampleString, sampleResult);
-        Assert.AreEqual(nullString, whitespaceResult);
-        Assert.AreEqual(nullString, emptyResult);
-        Assert.AreEqual(nullString, nullResult);
-    }
-
     /// <summary>
     ///     Tests <see cref="StringExtensions.Base64Decode" />.
     /// </summary>
@@ -81,78 +37,6 @@ public class StringTests
         Assert.AreEqual(expected, result);
     }
 
-    /// <summary>
-    ///     Tests <see cref="StringExtensions.IsLower" />.
-    /// </summary>
-    [TestMethod]
-    public void IsLower()
-    {
-        const string inputA = "Hello World";
-        const string inputB = "hello world";
-        const string? nullString = null;
-
-        bool resultA = inputA.IsLower();
-        bool resultB = inputB.IsLower();
-
-        Assert.ThrowsException<ArgumentNullException>(() => nullString!.IsLower());
-        Assert.IsFalse(resultA);
-        Assert.IsTrue(resultB);
-    }
-
-    [TestMethod]
-    public void IsPalindrome()
-    {
-        const string inputA = "Race car";
-        const string inputB = "Racecar";
-        const string inputC = "A man, a plan, a canal, panama";
-        const string inputD = "Jackdaws love my big sphinx of quartz";
-        const string inputE = "Y";
-        const string inputF = "1";
-        const string inputG = "";
-
-        Assert.IsTrue(inputA.IsPalindrome(), inputA);
-        Assert.IsTrue(inputB.IsPalindrome(), inputB);
-        Assert.IsTrue(inputC.IsPalindrome(), inputC);
-        Assert.IsFalse(inputD.IsPalindrome(), inputD);
-        Assert.IsTrue(inputE.IsPalindrome(), inputE);
-        Assert.IsTrue(inputF.IsPalindrome(), inputF);
-        Assert.IsFalse(inputG.IsPalindrome(), inputG);
-    }
-
-    /// <summary>
-    ///     Tests <see cref="StringExtensions.IsUpper" />.
-    /// </summary>
-    [TestMethod]
-    public void IsUpper()
-    {
-        const string inputA = "Hello World";
-        const string inputB = "HELLO WORLD";
-        const string? nullString = null;
-
-        bool resultA = inputA.IsUpper();
-        bool resultB = inputB.IsUpper();
-
-        Assert.ThrowsException<ArgumentNullException>(() => nullString!.IsUpper());
-        Assert.IsFalse(resultA);
-        Assert.IsTrue(resultB);
-    }
-
-    /// <summary>
-    ///     Tests <see cref="StringExtensions.Shuffled(string, Random)" />.
-    /// </summary>
-    [TestMethod]
-    public void Shuffled()
-    {
-        const string input = "Hello World";
-        const string expected = " oHlldrWoel";
-        var random = new Random(1);
-
-        string result = input.Shuffled(random);
-
-        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null)!.Shuffled());
-        Assert.AreEqual(expected, result);
-    }
-
     /// <summary>
     ///     Tests <see cref="StringExtensions.Randomize" />.
     /// </summary>
@@ -170,66 +54,4 @@ public class StringTests
         Assert.AreEqual(string.Empty, string.Empty.Randomize(0));
         Assert.AreEqual(expected, result);
     }
-
-    /// <summary>
-    ///     Tests <see cref="StringExtensions.Repeat" />.
-    /// </summary>
-    [TestMethod]
-    public void Repeat()
-    {
-        const string input = "Hello World";
-        const string expected = "Hello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello World";
-        const int repeatCount = 8;
-
-        string result = input.Repeat(repeatCount);
-
-        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null)!.Repeat(repeatCount));
-        Assert.ThrowsException<ArgumentOutOfRangeException>(() => input.Repeat(-1));
-        Assert.AreEqual(expected, result);
-    }
-
-    /// <summary>
-    ///     Tests <see cref="StringExtensions.Repeat" />.
-    /// </summary>
-    [TestMethod]
-    public void Reverse()
-    {
-        const string input = "Hello World";
-        const string expected = "dlroW olleH";
-
-        string result = input.Reverse();
-
-        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null)!.Reverse());
-        Assert.AreEqual(string.Empty.Reverse(), string.Empty);
-        Assert.AreEqual(" ".Reverse(), " ");
-        Assert.AreEqual(expected, result);
-    }
-
-    /// <summary>
-    ///     Tests <see cref="StringExtensions.WithEmptyAlternative" /> and
-    ///     <see cref="StringExtensions.WithWhiteSpaceAlternative"/>.
-    /// </summary>
-    [TestMethod]
-    public void WithAlternative()
-    {
-        const string inputA = "Hello World";
-        const string inputB = " ";
-        const string inputC = "";
-        const string? inputD = null;
-        const string alternative = "ALTERNATIVE";
-
-        string resultA = inputA.WithEmptyAlternative(alternative);
-        string resultB = inputB.WithEmptyAlternative(alternative);
-        string resultBWithWhitespace = inputB.WithWhiteSpaceAlternative(alternative);
-        string resultC = inputC.WithEmptyAlternative(alternative);
-        string resultD = inputD.WithEmptyAlternative(alternative);
-
-        Assert.AreEqual(resultA, inputA);
-        Assert.AreEqual(resultB, inputB);
-        Assert.AreEqual(resultBWithWhitespace, alternative);
-        Assert.AreEqual(resultC, alternative);
-        Assert.AreEqual(resultD, alternative);
-        Assert.AreEqual(alternative, ((string?)null).WithEmptyAlternative(alternative));
-        Assert.AreEqual(alternative, ((string?)null).WithWhiteSpaceAlternative(alternative));
-    }
 }

X10D.Tests/src/Text/StringTests.cs

@@ -7,10 +7,42 @@ namespace X10D.Tests.Text;
 [TestClass]
 public class StringTests
 {
-    private struct SampleStructure
+    [TestMethod]
+    public void AsNullIfEmptyShouldBeCorrect()
     {
-        [JsonPropertyName("values")]
+        const string sampleString = "Hello World";
-        public int[] Values { get; set; }
+        const string whitespaceString = " ";
+        const string emptyString = "";
+        const string? nullString = null;
+
+        string sampleResult = sampleString.AsNullIfEmpty();
+        string whitespaceResult = whitespaceString.AsNullIfEmpty();
+        string emptyResult = emptyString.AsNullIfEmpty();
+        string? nullResult = nullString.AsNullIfEmpty();
+
+        Assert.AreEqual(sampleString, sampleResult);
+        Assert.AreEqual(whitespaceString, whitespaceResult);
+        Assert.AreEqual(nullString, emptyResult);
+        Assert.AreEqual(nullString, nullResult);
+    }
+
+    [TestMethod]
+    public void AsNullIfWhiteSpaceShouldBeCorrect()
+    {
+        const string sampleString = "Hello World";
+        const string whitespaceString = " ";
+        const string emptyString = "";
+        const string? nullString = null;
+
+        string sampleResult = sampleString.AsNullIfWhiteSpace();
+        string whitespaceResult = whitespaceString.AsNullIfWhiteSpace();
+        string emptyResult = emptyString.AsNullIfWhiteSpace();
+        string? nullResult = nullString.AsNullIfWhiteSpace();
+
+        Assert.AreEqual(sampleString, sampleResult);
+        Assert.AreEqual(nullString, whitespaceResult);
+        Assert.AreEqual(nullString, emptyResult);
+        Assert.AreEqual(nullString, nullResult);
     }
 
     [TestMethod]
@@ -26,4 +58,174 @@ public class StringTests
         Assert.AreEqual(2, target.Values[1]);
         Assert.AreEqual(3, target.Values[2]);
     }
+
+    [TestMethod]
+    public void IsLowerShouldBeCorrect()
+    {
+        Assert.IsTrue("hello world".IsLower());
+        Assert.IsFalse("HELLO WORLD".IsLower());
+        Assert.IsFalse("Hello World".IsLower());
+    }
+
+    [TestMethod]
+    public void IsLowerNullShouldThrow()
+    {
+        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null)!.IsLower());
+    }
+
+    [TestMethod]
+    public void IsPalindromeShouldBeCorrect()
+    {
+        const string inputA = "Race car";
+        const string inputB = "Racecar";
+        const string inputC = "A man, a plan, a canal, panama";
+        const string inputD = "Jackdaws love my big sphinx of quartz";
+        const string inputE = "Y";
+        const string inputF = "1";
+
+        Assert.IsTrue(inputA.IsPalindrome(), inputA);
+        Assert.IsTrue(inputB.IsPalindrome(), inputB);
+        Assert.IsTrue(inputC.IsPalindrome(), inputC);
+        Assert.IsFalse(inputD.IsPalindrome(), inputD);
+        Assert.IsTrue(inputE.IsPalindrome(), inputE);
+        Assert.IsTrue(inputF.IsPalindrome(), inputF);
+    }
+
+    [TestMethod]
+    public void IsPalindromeEmptyShouldBeFalse()
+    {
+        Assert.IsFalse(string.Empty.IsPalindrome());
+    }
+
+    [TestMethod]
+    public void IsPalindromeNullShouldThrow()
+    {
+        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null)!.IsPalindrome());
+    }
+
+    [TestMethod]
+    public void IsUpperShouldBeCorrect()
+    {
+        Assert.IsTrue("HELLO WORLD".IsUpper());
+        Assert.IsFalse("hello world".IsUpper());
+        Assert.IsFalse("Hello World".IsUpper());
+    }
+
+    [TestMethod]
+    public void IsUpperNullShouldThrow()
+    {
+        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null)!.IsUpper());
+    }
+
+    [TestMethod]
+    public void RepeatShouldBeCorrect()
+    {
+        const string expected = "aaaaaaaaaa";
+        string actual = "a".Repeat(10);
+
+        Assert.AreEqual(expected, actual);
+    }
+
+    [TestMethod]
+    public void RepeatOneCountShouldBeLength1String()
+    {
+        string repeated = "a".Repeat(1);
+        Assert.AreEqual(1, repeated.Length);
+        Assert.AreEqual("a", repeated);
+    }
+
+    [TestMethod]
+    public void RepeatZeroCountShouldBeEmpty()
+    {
+        Assert.AreEqual(string.Empty, "a".Repeat(0));
+    }
+
+    [TestMethod]
+    public void RepeatNegativeCountShouldThrow()
+    {
+        Assert.ThrowsException<ArgumentOutOfRangeException>(() => "a".Repeat(-1));
+    }
+
+    [TestMethod]
+    public void RepeatNullShouldThrow()
+    {
+        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null)!.Repeat(0));
+    }
+
+    [TestMethod]
+    public void ReverseShouldBeCorrect()
+    {
+        const string input = "Hello World";
+        const string expected = "dlroW olleH";
+
+        string result = input.Reverse();
+
+        Assert.AreEqual(string.Empty.Reverse(), string.Empty);
+        Assert.AreEqual(" ".Reverse(), " ");
+        Assert.AreEqual(expected, result);
+    }
+
+    [TestMethod]
+    public void ReverseNullShouldThrow()
+    {
+        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null)!.Reverse());
+    }
+
+    [TestMethod]
+    public void ShuffleShouldReorder()
+    {
+        const string alphabet = "abcdefghijklmnopqrstuvwxyz";
+        string shuffled = alphabet;
+
+        Assert.AreEqual(alphabet, shuffled);
+
+        shuffled = alphabet.Shuffled();
+
+        Assert.AreNotEqual(alphabet, shuffled);
+    }
+
+    [TestMethod]
+    public void NullShuffleShouldThrow()
+    {
+        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null)!.Shuffled());
+    }
+
+    [TestMethod]
+    public void WithEmptyAlternativeShouldBeCorrect()
+    {
+        const string inputA = "Hello World";
+        const string inputB = " ";
+        const string inputC = "";
+        const string? inputD = null;
+        const string alternative = "ALTERNATIVE";
+
+        string resultA = inputA.WithEmptyAlternative(alternative);
+        string resultB = inputB.WithEmptyAlternative(alternative);
+        string resultC = inputC.WithEmptyAlternative(alternative);
+        string resultD = inputD.WithEmptyAlternative(alternative);
+
+        Assert.AreEqual(resultA, inputA);
+        Assert.AreEqual(resultB, inputB);
+        Assert.AreEqual(resultC, alternative);
+        Assert.AreEqual(resultD, alternative);
+        Assert.AreEqual(alternative, ((string?)null).WithEmptyAlternative(alternative));
+    }
+
+    [TestMethod]
+    public void WithWhiteSpaceAlternativeShouldBeCorrect()
+    {
+        const string input = " ";
+        const string alternative = "ALTERNATIVE";
+
+        string result = input.WithWhiteSpaceAlternative(alternative);
+
+        Assert.AreEqual(result, alternative);
+        Assert.AreEqual(alternative, ((string?)null).WithWhiteSpaceAlternative(alternative));
+    }
+
+    private struct SampleStructure
+    {
+        [JsonPropertyName("values")]
+        public int[] Values { get; set; }
+    }
 }

X10D/src/Collections/ArrayExtensions.cs

@@ -1,4 +1,4 @@
-namespace X10D;
+namespace X10D.Collections;
 
 /// <summary>
 ///     Extension methods for <see cref="Array" />.

X10D/src/StringExtensions/StringExtensions.cs

@@ -1,6 +1,4 @@
-using System.Diagnostics.CodeAnalysis;
 using System.Text;
-using X10D.Collections;
 
 namespace X10D;
 
@@ -9,35 +7,6 @@ namespace X10D;
 /// </summary>
 public static class StringExtensions
 {
-    /// <summary>
-    ///     Normalizes a string which may be either <see langword="null" /> or empty to <see langword="null" />.
-    /// </summary>
-    /// <param name="value">The value to normalize.</param>
-    /// <returns>
-    ///     <see langword="null" /> if <paramref name="value" /> is <see langword="null" /> or empty; otherwise,
-    ///     <paramref name="value" />.
-    /// </returns>
-    [return: NotNullIfNotNull("value")]
-    public static string? AsNullIfEmpty(this string? value)
-    {
-        return value.WithEmptyAlternative(null);
-    }
-
-    /// <summary>
-    ///     Normalizes a string which may be either <see langword="null" />, empty, or consisting of only whitespace, to
-    ///     <see langword="null" />.
-    /// </summary>
-    /// <param name="value">The value to normalize.</param>
-    /// <returns>
-    ///     <see langword="null" /> if <paramref name="value" /> is <see langword="null" />, empty, or consists of only
-    ///     whitespace; otherwise, <paramref name="value" />.
-    /// </returns>
-    [return: NotNullIfNotNull("value")]
-    public static string? AsNullIfWhiteSpace(this string? value)
-    {
-        return value.WithWhiteSpaceAlternative(null);
-    }
-
     /// <summary>
     ///     Converts the specified string, which encodes binary data as base-64 digits, to an equivalent plain text string.
     /// </summary>
@@ -188,117 +157,6 @@ public static class StringExtensions
         return encoding.GetBytes(value);
     }
 
-    /// <summary>
-    ///     Determines if all alpha characters in this string are considered lowercase.
-    /// </summary>
-    /// <param name="value">The input string.</param>
-    /// <returns>
-    ///     Returns <see langword="true" /> if all alpha characters are lowercase, <see langword="false" />
-    ///     otherwise.
-    /// </returns>
-    public static bool IsLower(this string value)
-    {
-        if (value is null)
-        {
-            throw new ArgumentNullException(nameof(value));
-        }
-
-        for (var index = 0; index < value.Length; index++)
-        {
-            if (!char.IsLetter(value[index]))
-            {
-                continue;
-            }
-
-            if (!char.IsLower(value[index]))
-            {
-                return false;
-            }
-        }
-
-        return true;
-    }
-
-    /// <summary>
-    ///     Determines whether the current string is considered palindromic; that is, the letters within the string are the
-    ///     same when reversed.
-    /// </summary>
-    /// <param name="value">The value to check.</param>
-    /// <returns>
-    ///     <see langword="true" /> if <paramref name="value" /> is considered a palindromic string; otherwise,
-    ///     <see langword="false" />.
-    /// </returns>
-    /// <exception cref="ArgumentNullException"><paramref name="value" /> is <see langword="null" />.</exception>
-    public static bool IsPalindrome(this string value)
-    {
-        if (value is null)
-        {
-            throw new ArgumentNullException(nameof(value));
-        }
-
-        if (string.IsNullOrWhiteSpace(value))
-        {
-            // empty string is not palindromic
-            return false;
-        }
-
-        for (int index = 0, endIndex = value.Length - 1; index < value.Length; index++, endIndex--)
-        {
-            Rune startRune = new Rune(value[index]);
-            Rune endRune = new Rune(value[endIndex]);
-
-            if (!Rune.IsLetter(startRune) && !Rune.IsNumber(startRune))
-            {
-                endIndex++;
-                continue;
-            }
-
-            if (!Rune.IsLetter(endRune) && !Rune.IsNumber(endRune))
-            {
-                index--;
-                continue;
-            }
-
-            if (Rune.ToUpperInvariant(startRune) != Rune.ToUpperInvariant(endRune))
-            {
-                return false;
-            }
-        }
-
-        return true;
-    }
-
-    /// <summary>
-    ///     Determines if all alpha characters in this string are considered uppercase.
-    /// </summary>
-    /// <param name="value">The input string.</param>
-    /// <returns>
-    ///     Returns <see langword="true" /> if all alpha characters are uppercase, <see langword="false" />
-    ///     otherwise.
-    /// </returns>
-    public static bool IsUpper(this string value)
-    {
-        if (value is null)
-        {
-            throw new ArgumentNullException(nameof(value));
-        }
-
-        for (var index = 0; index < value.Length; index++)
-        {
-            if (!char.IsLetter(value[index]))
-            {
-                continue;
-            }
-
-            if (!char.IsUpper(value[index]))
-            {
-                return false;
-            }
-        }
-
-        return true;
-    }
-
     /// <summary>
     ///     Returns a new string of a specified length by randomly selecting characters from the current string.
     /// </summary>
@@ -342,102 +200,6 @@ public static class StringExtensions
         return builder.ToString();
     }
 
-    /// <summary>
-    ///     Repeats a string a specified number of times.
-    /// </summary>
-    /// <param name="value">The string to repeat.</param>
-    /// <param name="count">The repeat count.</param>
-    /// <returns>A string containing <paramref name="value" /> repeated <paramref name="count" /> times.
-    /// </returns>
-    /// <exception cref="ArgumentNullException"><paramref name="value" /> is <see langword="null" />.</exception>
-    public static string Repeat(this string value, int count)
-    {
-        if (value is null)
-        {
-            throw new ArgumentNullException(nameof(value));
-        }
-
-        if (count < 0)
-        {
-            throw new ArgumentOutOfRangeException(nameof(count), ExceptionMessages.CountMustBeGreaterThanOrEqualTo0);
-        }
-
-        var builder = new StringBuilder(value.Length * count);
-
-        for (var i = 0; i < count; i++)
-        {
-            builder.Append(value);
-        }
-
-        return builder.ToString();
-    }
-
-    /// <summary>
-    ///     Reverses the current string.
-    /// </summary>
-    /// <param name="value">The string to reverse.</param>
-    /// <returns>A <see cref="string" /> whose characters are that of <paramref name="value" /> in reverse order.</returns>
-    public static string Reverse(this string value)
-    {
-        if (value is null)
-        {
-            throw new ArgumentNullException(nameof(value));
-        }
-
-        if (value.Length < 2)
-        {
-            return value;
-        }
-
-        unsafe
-        {
-            char* array = stackalloc char[value.Length];
-
-            for (var index = 0; index < value.Length; index++)
-            {
-                array[index] = value[value.Length - index - 1];
-            }
-
-            return new string(array);
-        }
-    }
-
-    /// <summary>
-    ///     Shuffles the characters in the string using the <see cref="Random.Shared" /> instance.
-    /// </summary>
-    /// <param name="value">The string to shuffle.</param>
-    /// <returns>A new <see cref="string" /> containing the characters in <paramref name="value" />, rearranged.</returns>
-    public static string Shuffled(this string value)
-    {
-        return value.Shuffled(Random.Shared);
-    }
-
-    /// <summary>
-    ///     Shuffles the characters in the string.
-    /// </summary>
-    /// <param name="value">The string to shuffle.</param>
-    /// <param name="random">The <see cref="System.Random" /> instance.</param>
-    /// <returns>A new <see cref="string" /> containing the characters in <paramref name="value" />, rearranged.</returns>
-    /// <exception cref="ArgumentNullException">
-    ///     <para><paramref name="value" /> is <see langword="null" />.</para>
-    ///     -or-
-    ///     <para><paramref name="random" /> is <see langword="null" />.</para>
-    /// </exception>
-    public static string Shuffled(this string value, Random random)
-    {
-        if (value is null)
-        {
-            throw new ArgumentNullException(nameof(value));
-        }
-
-        if (random is null)
-        {
-            throw new ArgumentNullException(nameof(random));
-        }
-
-        return new string(value.ToCharArray().Shuffled(random).ToArray());
-    }
-
     /// <summary>
     ///     Splits the <see cref="string" /> into chunks that are no greater than <paramref name="chunkSize" /> in length.
     /// </summary>
@@ -478,35 +240,4 @@ public static class StringExtensions
             ? result
             : default;
     }
-
-    /// <summary>
-    ///     Normalizes a string which may be either <see langword="null" /> or empty to a specified alternative.
-    /// </summary>
-    /// <param name="value">The value to normalize.</param>
-    /// <param name="alternative">The alternative string.</param>
-    /// <returns>
-    ///     <paramref name="alternative" /> if <paramref name="value" /> is <see langword="null" /> or empty; otherwise,
-    ///     <paramref name="value" />.
-    /// </returns>
-    [return: NotNullIfNotNull("alternative")]
-    public static string? WithEmptyAlternative(this string? value, string? alternative)
-    {
-        return string.IsNullOrEmpty(value) ? alternative : value;
-    }
-
-    /// <summary>
-    ///     Normalizes a string which may be either <see langword="null" />, empty, or consisting of only whitespace, to a
-    ///     specified alternative.
-    /// </summary>
-    /// <param name="value">The value to normalize.</param>
-    /// <param name="alternative">The alternative string.</param>
-    /// <returns>
-    ///     <paramref name="alternative" /> if <paramref name="value" /> is <see langword="null" />, empty, or consists of only
-    ///     whitespace; otherwise, <paramref name="value" />.
-    /// </returns>
-    [return: NotNullIfNotNull("alternative")]
-    public static string? WithWhiteSpaceAlternative(this string? value, string? alternative)
-    {
-        return string.IsNullOrWhiteSpace(value) ? alternative : value;
-    }
 }

X10D/src/Text/CharExtensions.cs

@@ -1,7 +1,7 @@
 namespace X10D.Text;
 
 /// <summary>
-///     Extension methods for <see cref="char" />.
+///     Text-related extension methods for <see cref="char" />.
 /// </summary>
 public static class CharExtensions
 {
@@ -15,21 +15,12 @@ public static class CharExtensions
     /// </returns>
     public static string Repeat(this char value, int count)
     {
-        if (count < 0)
+        return count switch
         {
-            throw new ArgumentOutOfRangeException(nameof(count), ExceptionMessages.CountMustBeGreaterThanOrEqualTo0);
+            < 0 => throw new ArgumentOutOfRangeException(nameof(count), ExceptionMessages.CountMustBeGreaterThanOrEqualTo0),
-        }
+            0 => string.Empty,
-
+            1 => value.ToString(),
-        if (count == 0)
+            _ => new string(value, count)
-        {
+        };
-            return string.Empty;
-        }
-
-        if (count == 1)
-        {
-            return value.ToString();
-        }
-
-        return new string(value, count);
     }
 }

X10D/src/Text/RuneExtensions.cs

@@ -3,7 +3,7 @@
 namespace X10D.Text;
 
 /// <summary>
-///     Extension methods for <see cref="Rune" />.
+///     Text-related extension methods for <see cref="Rune" />.
 /// </summary>
 public static class RuneExtensions
 {
@@ -17,18 +17,13 @@ public static class RuneExtensions
     /// </returns>
     public static string Repeat(this Rune value, int count)
     {
-        if (count < 0)
+        switch (count)
         {
+            case < 0:
                 throw new ArgumentOutOfRangeException(nameof(count), ExceptionMessages.CountMustBeGreaterThanOrEqualTo0);
-        }
+            case 0:
-
-        if (count == 0)
-        {
                 return string.Empty;
-        }
+            case 1:
-
-        if (count == 1)
-        {
                 return value.ToString();
         }
 

X10D/src/Text/StringExtensions.cs

@@ -1,4 +1,7 @@
-using System.Text.Json;
+using System.Diagnostics.CodeAnalysis;
+using System.Text;
+using System.Text.Json;
+using X10D.Collections;
 
 namespace X10D.Text;
 
@@ -7,6 +10,35 @@ namespace X10D.Text;
 /// </summary>
 public static class StringExtensions
 {
+    /// <summary>
+    ///     Normalizes a string which may be either <see langword="null" /> or empty to <see langword="null" />.
+    /// </summary>
+    /// <param name="value">The value to normalize.</param>
+    /// <returns>
+    ///     <see langword="null" /> if <paramref name="value" /> is <see langword="null" /> or empty; otherwise,
+    ///     <paramref name="value" />.
+    /// </returns>
+    [return: NotNullIfNotNull("value")]
+    public static string? AsNullIfEmpty(this string? value)
+    {
+        return value.WithEmptyAlternative(null);
+    }
+
+    /// <summary>
+    ///     Normalizes a string which may be either <see langword="null" />, empty, or consisting of only whitespace, to
+    ///     <see langword="null" />.
+    /// </summary>
+    /// <param name="value">The value to normalize.</param>
+    /// <returns>
+    ///     <see langword="null" /> if <paramref name="value" /> is <see langword="null" />, empty, or consists of only
+    ///     whitespace; otherwise, <paramref name="value" />.
+    /// </returns>
+    [return: NotNullIfNotNull("value")]
+    public static string? AsNullIfWhiteSpace(this string? value)
+    {
+        return value.WithWhiteSpaceAlternative(null);
+    }
+
     /// <summary>
     ///     Returns an object from the specified JSON string.
     /// </summary>
@@ -20,4 +52,236 @@ public static class StringExtensions
     {
         return JsonSerializer.Deserialize<T>(value, options);
     }
+
+    /// <summary>
+    ///     Determines if all alpha characters in this string are considered lowercase.
+    /// </summary>
+    /// <param name="value">The input string.</param>
+    /// <returns>
+    ///     Returns <see langword="true" /> if all alpha characters are lowercase, <see langword="false" />
+    ///     otherwise.
+    /// </returns>
+    public static bool IsLower(this string value)
+    {
+        if (value is null)
+        {
+            throw new ArgumentNullException(nameof(value));
+        }
+
+        for (var index = 0; index < value.Length; index++)
+        {
+            var rune = new Rune(value[index]);
+
+            if (!Rune.IsLetter(rune))
+            {
+                continue;
+            }
+
+            if (!Rune.IsLower(rune))
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /// <summary>
+    ///     Determines whether the current string is considered palindromic; that is, the letters within the string are the
+    ///     same when reversed.
+    /// </summary>
+    /// <param name="value">The value to check.</param>
+    /// <returns>
+    ///     <see langword="true" /> if <paramref name="value" /> is considered a palindromic string; otherwise,
+    ///     <see langword="false" />.
+    /// </returns>
+    /// <exception cref="ArgumentNullException"><paramref name="value" /> is <see langword="null" />.</exception>
+    public static bool IsPalindrome(this string value)
+    {
+        if (value is null)
+        {
+            throw new ArgumentNullException(nameof(value));
+        }
+
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            // empty string is not palindromic
+            return false;
+        }
+
+        for (int index = 0, endIndex = value.Length - 1; index < value.Length; index++, endIndex--)
+        {
+            Rune startRune = new Rune(value[index]);
+            Rune endRune = new Rune(value[endIndex]);
+
+            if (!Rune.IsLetter(startRune) && !Rune.IsNumber(startRune))
+            {
+                endIndex++;
+                continue;
+            }
+
+            if (!Rune.IsLetter(endRune) && !Rune.IsNumber(endRune))
+            {
+                index--;
+                continue;
+            }
+
+            if (Rune.ToUpperInvariant(startRune) != Rune.ToUpperInvariant(endRune))
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /// <summary>
+    ///     Determines if all alpha characters in this string are considered uppercase.
+    /// </summary>
+    /// <param name="value">The input string.</param>
+    /// <returns>
+    ///     Returns <see langword="true" /> if all alpha characters are uppercase, <see langword="false" />
+    ///     otherwise.
+    /// </returns>
+    public static bool IsUpper(this string value)
+    {
+        if (value is null)
+        {
+            throw new ArgumentNullException(nameof(value));
+        }
+
+        for (var index = 0; index < value.Length; index++)
+        {
+            var rune = new Rune(value[index]);
+
+            if (!Rune.IsLetter(rune))
+            {
+                continue;
+            }
+
+            if (!Rune.IsUpper(rune))
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /// <summary>
+    ///     Repeats a string a specified number of times.
+    /// </summary>
+    /// <param name="value">The string to repeat.</param>
+    /// <param name="count">The repeat count.</param>
+    /// <returns>A string containing <paramref name="value" /> repeated <paramref name="count" /> times.
+    /// </returns>
+    /// <exception cref="ArgumentNullException"><paramref name="value" /> is <see langword="null" />.</exception>
+    public static string Repeat(this string value, int count)
+    {
+        if (value is null)
+        {
+            throw new ArgumentNullException(nameof(value));
+        }
+
+        switch (count)
+        {
+            case < 0:
+                throw new ArgumentOutOfRangeException(nameof(count), ExceptionMessages.CountMustBeGreaterThanOrEqualTo0);
+            case 0:
+                return string.Empty;
+            case 1:
+                return value;
+        }
+
+        var builder = new StringBuilder(value.Length * count);
+
+        for (var i = 0; i < count; i++)
+        {
+            builder.Append(value);
+        }
+
+        return builder.ToString();
+    }
+
+    /// <summary>
+    ///     Reverses the current string.
+    /// </summary>
+    /// <param name="value">The string to reverse.</param>
+    /// <returns>A <see cref="string" /> whose characters are that of <paramref name="value" /> in reverse order.</returns>
+    public static string Reverse(this string value)
+    {
+        if (value is null)
+        {
+            throw new ArgumentNullException(nameof(value));
+        }
+
+        if (value.Length < 2)
+        {
+            return value;
+        }
+
+        Span<char> span = stackalloc char[value.Length];
+
+        for (var index = 0; index < value.Length; index++)
+        {
+            span[index] = value[value.Length - index - 1];
+        }
+
+        return new string(span);
+    }
+
+    /// <summary>
+    ///     Shuffles the characters in the string.
+    /// </summary>
+    /// <param name="value">The string to shuffle.</param>
+    /// <param name="random">
+    ///     The <see cref="System.Random" /> instance to use for the shuffling. If <see langword="null" /> is specified,
+    ///     <see cref="System.Random.Shared" /> is used.
+    /// </param>
+    /// <returns>A new <see cref="string" /> containing the characters in <paramref name="value" />, rearranged.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="value" /> is <see langword="null" />.</exception>
+    public static string Shuffled(this string value, Random? random = null)
+    {
+        if (value is null)
+        {
+            throw new ArgumentNullException(nameof(value));
+        }
+
+        random ??= Random.Shared;
+
+        char[] array = value.ToCharArray();
+        array.Shuffle(random);
+        return new string(array);
+    }
+
+    /// <summary>
+    ///     Normalizes a string which may be either <see langword="null" /> or empty to a specified alternative.
+    /// </summary>
+    /// <param name="value">The value to normalize.</param>
+    /// <param name="alternative">The alternative string.</param>
+    /// <returns>
+    ///     <paramref name="alternative" /> if <paramref name="value" /> is <see langword="null" /> or empty; otherwise,
+    ///     <paramref name="value" />.
+    /// </returns>
+    [return: NotNullIfNotNull("alternative")]
+    public static string? WithEmptyAlternative(this string? value, string? alternative)
+    {
+        return string.IsNullOrEmpty(value) ? alternative : value;
+    }
+
+    /// <summary>
+    ///     Normalizes a string which may be either <see langword="null" />, empty, or consisting of only whitespace, to a
+    ///     specified alternative.
+    /// </summary>
+    /// <param name="value">The value to normalize.</param>
+    /// <param name="alternative">The alternative string.</param>
+    /// <returns>
+    ///     <paramref name="alternative" /> if <paramref name="value" /> is <see langword="null" />, empty, or consists of only
+    ///     whitespace; otherwise, <paramref name="value" />.
+    /// </returns>
+    [return: NotNullIfNotNull("alternative")]
+    public static string? WithWhiteSpaceAlternative(this string? value, string? alternative)
+    {
+        return string.IsNullOrWhiteSpace(value) ? alternative : value;
+    }
 }