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Merged
Antyss77 merged 1 commit into from
Aug 7, 2026
Merged

perf: use ArrayPool for large buffers, simplify null-forwarding via A… #8

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135 changes: 84 additions & 51 deletions StringExtension/StringExtension.cs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
using System.Text.RegularExpressions;
using System.Buffers;
using System.Text.RegularExpressions;

namespace StringExtension;

Expand All @@ -7,6 +8,12 @@ namespace StringExtension;
/// </summary>
public static partial class StringExtension
{
/// <summary>
/// Above this length, buffers are rented from <see cref="ArrayPool{T}"/> instead
/// of stack-allocated, to avoid excessive stack usage for large inputs.
/// </summary>
private const int StackAllocThreshold = 256;

/// <summary>
/// Represents a regular expression that can be used to validate an email address.
/// </summary>
Expand All @@ -27,6 +34,7 @@ public static partial class StringExtension
/// <param name="input">The input string.</param>
/// <param name="charactersToRemove">An array of characters to remove.</param>
/// <returns>A new string with specified characters removed.</returns>
/// <remarks>Returns <see langword="null"/> if <paramref name="input"/> is <see langword="null"/>.</remarks>
public static string RemoveCharacters(this string input, char[] charactersToRemove)
{
if (string.IsNullOrEmpty(input) || charactersToRemove is null || charactersToRemove.Length == 0)
Expand All @@ -50,18 +58,31 @@ public static string RemoveCharacters(this ReadOnlySpan<char> input, ReadOnlySpa
return input.ToString();
}

Span<char> buffer = input.Length <= 256 ? stackalloc char[input.Length] : new char[input.Length];
var count = 0;
char[]? pooledBuffer = null;
Span<char> buffer = (uint)input.Length <= StackAllocThreshold
? stackalloc char[input.Length]
: (pooledBuffer = ArrayPool<char>.Shared.Rent(input.Length));

foreach (var c in input)
try
{
var count = 0;
foreach (var c in input)
{
if (charactersToRemove.IndexOf(c) < 0)
{
buffer[count++] = c;
}
}

return new string(buffer[..count]);
}
finally
{
if (charactersToRemove.IndexOf(c) < 0)
if (pooledBuffer is not null)
{
buffer[count++] = c;
ArrayPool<char>.Shared.Return(pooledBuffer);
}
}

return new string(buffer[..count]);
}

/// <summary>
Expand Down Expand Up @@ -112,11 +133,6 @@ public static bool IsValidPhoneNumber(this ReadOnlySpan<char> phoneNumber)
/// <returns>The number of occurrences of the substring in the input string.</returns>
public static int CountSubstring(this string input, string substring)
{
if (string.IsNullOrEmpty(input) || string.IsNullOrEmpty(substring))
{
return 0;
}

return CountSubstring(input.AsSpan(), substring.AsSpan());
}

Expand All @@ -142,15 +158,14 @@ public static int CountSubstring(this ReadOnlySpan<char> input, ReadOnlySpan<cha
/// </summary>
/// <param name="input">The input to reverse words.</param>
/// <returns>The input string with the order of words reversed.</returns>
/// <remarks>Returns <see langword="null"/> if <paramref name="input"/> is <see langword="null"/>.</remarks>
public static string ReverseWords(this string input)
{
if (string.IsNullOrEmpty(input))
{
return input;
}

// string.Create needs the length up front, and it is preserved by a
// simple word swap around single-space separators.
return string.Create(input.Length, input, static (span, source) =>
{
foreach (Range word in source.AsSpan().Split(' '))
Expand Down Expand Up @@ -179,7 +194,7 @@ public static string ReverseWords(this string input)
/// <returns><c>true</c> if the string is a palindrome; otherwise, <c>false</c>.</returns>
public static bool IsPalindrome(this string input)
{
return !string.IsNullOrEmpty(input) && IsPalindrome(input.AsSpan());
return IsPalindrome(input.AsSpan());
}

/// <summary>
Expand Down Expand Up @@ -231,11 +246,6 @@ public static bool IsPalindrome(this ReadOnlySpan<char> input)
/// <returns>The number of letters in the input string.</returns>
public static int CountLetters(this string input)
{
if (string.IsNullOrEmpty(input))
{
return 0;
}

return CountLetters(input.AsSpan());
}

Expand Down Expand Up @@ -263,6 +273,7 @@ public static int CountLetters(this ReadOnlySpan<char> input)
/// </summary>
/// <param name="input">The input string.</param>
/// <returns>A new string with duplicate characters removed.</returns>
/// <remarks>Returns <see langword="null"/> if <paramref name="input"/> is <see langword="null"/>.</remarks>
public static string RemoveDuplicateCharacters(this string input)
{
if (string.IsNullOrEmpty(input))
Expand All @@ -286,19 +297,33 @@ public static string RemoveDuplicateCharacters(this ReadOnlySpan<char> input)
return string.Empty;
}

Span<char> buffer = input.Length <= 256 ? stackalloc char[input.Length] : new char[input.Length];
var seen = new HashSet<char>(input.Length);
var count = 0;
char[]? pooledBuffer = null;
Span<char> buffer = (uint)input.Length <= StackAllocThreshold
? stackalloc char[input.Length]
: (pooledBuffer = ArrayPool<char>.Shared.Rent(input.Length));

foreach (var c in input)
try
{
if (seen.Add(c))
var seen = new HashSet<char>(input.Length);
var count = 0;

foreach (var c in input)
{
buffer[count++] = c;
if (seen.Add(c))
{
buffer[count++] = c;
}
}
}

return new string(buffer[..count]);
return new string(buffer[..count]);
}
finally
{
if (pooledBuffer is not null)
{
ArrayPool<char>.Shared.Return(pooledBuffer);
}
}
}

/// <summary>
Expand All @@ -308,11 +333,6 @@ public static string RemoveDuplicateCharacters(this ReadOnlySpan<char> input)
/// <returns>The input string converted to camel case.</returns>
public static string ToCamelCase(this string input)
{
if (string.IsNullOrEmpty(input))
{
return string.Empty;
}

return ToCamelCase(input.AsSpan());
}

Expand All @@ -328,30 +348,43 @@ public static string ToCamelCase(this ReadOnlySpan<char> input)
return string.Empty;
}

Span<char> buffer = input.Length <= 256 ? stackalloc char[input.Length] : new char[input.Length];

var count = 0;
var shouldCapitalize = false;
char[]? pooledBuffer = null;
Span<char> buffer = (uint)input.Length <= StackAllocThreshold
? stackalloc char[input.Length]
: (pooledBuffer = ArrayPool<char>.Shared.Rent(input.Length));

foreach (var c in input)
try
{
if (char.IsWhiteSpace(c) || c == '_')
var count = 0;
var shouldCapitalize = false;

foreach (var c in input)
{
shouldCapitalize = true;
continue;
if (char.IsWhiteSpace(c) || c == '_')
{
shouldCapitalize = true;
continue;
}

buffer[count++] = shouldCapitalize ? char.ToUpperInvariant(c) : char.ToLowerInvariant(c);
shouldCapitalize = false;
}

buffer[count++] = shouldCapitalize ? char.ToUpperInvariant(c) : char.ToLowerInvariant(c);
shouldCapitalize = false;
}
// The very first character is always lowercase, even if the input
// started with a separator (e.g. "_hello" gives "hello", not "Hello").
if (count > 0)
{
buffer[0] = char.ToLowerInvariant(buffer[0]);
}

// The very first character is always lowercase, even if the input
// started with a separator (e.g. "_hello" gives "hello", not "Hello").
if (count > 0)
return new string(buffer[..count]);
}
finally
{
buffer[0] = char.ToLowerInvariant(buffer[0]);
if (pooledBuffer is not null)
{
ArrayPool<char>.Shared.Return(pooledBuffer);
}
}

return new string(buffer[..count]);
}
}
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