Reduced allocations in string.MaxLength

Kaoticz · Sep 16, 2023 · 32f281a · 32f281a
1 parent c91219c
commit 32f281a
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Showing 3 changed files with 58 additions and 9 deletions.
diff --git a/Kotz.Extensions/ReadOnlySpanCharExt.cs b/Kotz.Extensions/ReadOnlySpanCharExt.cs
@@ -129,4 +129,14 @@ public static bool HasFirstWordOf(this ReadOnlySpan<char> text, ReadOnlySpan<cha
 
         return firstTextWord.Equals(firstSampleWord, comparisonType);
     }
+
+    /// <summary>
+    /// Truncates the string to the maximum specified length.
+    /// </summary>
+    /// <param name="text">This string.</param>
+    /// <param name="maxLength">The maximum length the string should have.</param>
+    /// <returns>This string with length equal to or lower than <paramref name="maxLength"/>.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Occurs when <paramref name="maxLength"/> is less than zero.</exception>
+    public static ReadOnlySpan<char> MaxLength(this ReadOnlySpan<char> text, int maxLength)
+        => text[..Math.Min(text.Length, maxLength)];
 }
diff --git a/Kotz.Extensions/StringExt.cs b/Kotz.Extensions/StringExt.cs
@@ -73,7 +73,18 @@ public static bool HasFirstWordOf(this string text, string sample, StringCompari
     /// <exception cref="ArgumentOutOfRangeException">Occurs when <paramref name="maxLength"/> is less than zero.</exception>
     [return: NotNullIfNotNull("text")]
     public static string? MaxLength(this string? text, int maxLength)
-        => text?[..Math.Min(text.Length, maxLength)];
+    {
+        if (maxLength < 0)
+            throw new ArgumentOutOfRangeException(nameof(maxLength), maxLength, "Maximum length cannot be less than 0.");
+        else if (string.IsNullOrWhiteSpace(text))
+            return text;
+
+        var result = ReadOnlySpanCharExt.MaxLength(text, maxLength);
+
+        return (result.Length == text.Length)
+            ? text
+            : result.ToString();
+    }
 
     /// <summary>
     /// Truncates the string to the maximum specified length.
@@ -83,12 +94,28 @@ public static bool HasFirstWordOf(this string text, string sample, StringCompari
     /// <param name="append">The string to be appended to the end of the truncated string.</param>
     /// <remarks>The <paramref name="append"/> only gets added to the truncated string if this string exceeds <paramref name="maxLength"/> in length.</remarks>
     /// <returns>This string with length equal to or lower than <paramref name="maxLength"/>.</returns>
-    /// <exception cref="ArgumentOutOfRangeException">Occurs when <paramref name="maxLength"/> is less than zero.</exception>
+    /// <exception cref="ArgumentOutOfRangeException">
+    /// Occurs when <paramref name="append"/> exceeds or is equal to <paramref name="maxLength"/>
+    /// or when <paramref name="maxLength"/> is less than zero.
+    /// </exception>
     [return: NotNullIfNotNull("text")]
     public static string? MaxLength(this string? text, int maxLength, string append)
-        => (text is null || text.Length <= maxLength)
-            ? text
-            : (text.MaxLength(Math.Max(0, maxLength - append.Length)) + append)[..maxLength];
+    {
+        if (text is null || text.Length <= maxLength)
+            return text;
+        else if (maxLength < 0)
+            throw new ArgumentOutOfRangeException(nameof(maxLength), maxLength, "Maximum length cannot be less than 0.");
+        else if (string.IsNullOrEmpty(append))
+            return text.MaxLength(maxLength);
+        else if (append.Length >= maxLength)
+            throw new ArgumentOutOfRangeException(nameof(append), append.Length, "Append exceeds or is equal to maximum length size.");
+
+        var truncatedText = ReadOnlySpanCharExt.MaxLength(text, maxLength);
+
+        return (truncatedText.Length == maxLength && truncatedText.Length - append.Length > 0)
+            ? truncatedText[..^append.Length].ToString() + append
+            : truncatedText.ToString();
+    }
 
     /// <summary>
     /// Converts a string to the "Title Case" format.

diff --git a/Kotz.Tests/Extensions/StringExtTest.cs b/Kotz.Tests/Extensions/StringExtTest.cs
@@ -8,20 +8,32 @@ public sealed class StringExtTest
     [InlineData(5, "hello", "hello")]
     [InlineData(5, "avocado", "avoca")]
     [InlineData(0, "banana", "")]
+    [InlineData(0, "", "")]
     [InlineData(5, null, null)]
     internal void MaxLengthTest(int length, string source, string result)
         => Assert.Equal(result, source.MaxLength(length));
 
     [Theory]
     [InlineData(11, "banana cheesecake", "banana[...]", "[...]")]
-    [InlineData(11, "banana chee", "banana chee", "[...]")]
     [InlineData(11, "banana chees", "banana[...]", "[...]")]
-    [InlineData(0, "banana", "", "[...]")]
+    [InlineData(11, "banana chee", "banana chee", "[...]")]
+    [InlineData(6, "banana cheesecake", "b[...]", "[...]")]
+    [InlineData(6, "banana", "banana", "[...]")]
+    [InlineData(1, "banana", "b", null)]
     [InlineData(5, "", "", "[...]")]
     [InlineData(5, "a", "a", "[...]")]
     [InlineData(5, "a", "a", null)]
-    internal void MaxLengthWithAppendTest(int length, string source, string result, string append)
-        => Assert.Equal(result, source.MaxLength(length, append));
+    [InlineData(5, null, null, null)]
+    [InlineData(5, null, null, "")]
+    internal void MaxLengthWithAppendTest(int maxLength, string source, string result, string append)
+        => Assert.Equal(result, source.MaxLength(maxLength, append));
+
+    [Theory]
+    [InlineData(0, "banana", "[...]")]
+    [InlineData(1, "banana", "[...]")]
+    [InlineData(5, "banana", "[...]")]
+    internal void MaxLengthWithAppendErrorTest(int maxLength, string source, string append)
+        => Assert.Throws<ArgumentOutOfRangeException>(() => source.MaxLength(maxLength, append));
 
     [Theory]
     [InlineData(null, null)]