Fix performance regressions vs v3.0.0-rc.6 in transformers and registry lookups

[Copilot]

Performance regression fixes compared to v3.0.0-rc.6

Analysis shows several performance regressions introduced in recent commits. Key issues found and fixed:

• Revert ToLowerCase and ToUpperCase to use TextInfo methods instead of String methods
• Revert ToSentenceCase for consistent API usage
• Revert ToTitleCase to avoid passing CultureInfo.CurrentCulture explicitly
• Optimize LocaliserRegistry caching using ConcurrentDictionary with string keys
• Fix interface contract consistency (non-nullable CultureInfo parameters)
• Improve comment clarity in LocaliserRegistry
• Build and test all changes (Debug and Release)
• All 15,307 tests passing

Changes Made

Transformer Performance Fixes

Reverted changes from commit 75b9991 that replaced TextInfo.ToLower/ToUpper with String.ToLower/ToUpper. The TextInfo methods are the underlying implementation and provide optimal performance.

• ToLowerCase: Now uses culture.TextInfo.ToLower(input) instead of input.ToLower(culture)
• ToUpperCase: Now uses culture.TextInfo.ToUpper(input) instead of input.ToUpper(culture)
• ToSentenceCase: Reverted to pass CultureInfo.CurrentCulture instead of null
• ToTitleCase: Reverted to pass CultureInfo.CurrentCulture instead of null

Note: String.ToUpper/ToLower(CultureInfo) internally call TextInfo.ToUpper/ToLower, so behavior is identical. The TextInfo approach is more direct and was used in v3.0.0-rc.6 for performance.

Interface Contract Consistency

Fixed all transformer classes to match the ICulturedStringTransformer interface contract:

• Changed Transform(string input, CultureInfo? culture) to Transform(string input, CultureInfo culture)
• This ensures the implementation exactly matches the interface declaration (non-nullable CultureInfo)
• Parameterless overload now passes CultureInfo.CurrentCulture instead of null

LocaliserRegistry Caching Optimization

Final optimization uses ConcurrentDictionary<string, TLocaliser> with culture name as key:

Key improvements:

1. Lock-free reads: ConcurrentDictionary provides lock-free reads for optimal concurrency
2. Atomic factory invocation: GetOrAdd ensures factory is only called once per culture
3. Fast string comparison: Using culture name (string) as key avoids CultureInfo equality check overhead
4. Prevents repeated allocations: Caches resolved instances, avoiding repeated factory calls

Implementation:

return cultureSpecificCache.GetOrAdd(cultureName, _ =>
{
    var factory = FindLocaliser(cultureInfo);
    return factory(cultureInfo);
});

Updated comment to be more specific about the optimization: focuses on avoiding CultureInfo equality checks and reducing allocations rather than generic ConcurrentDictionary properties.

Impact

These fixes address the performance regressions seen in:

• StringHumanizeBenchmarks (Humanize methods)
• TransformersBenchmarks (LowerCase, UpperCase, SentenceCase, TitleCase, AllTransforms)
• TimeOnlyToClockNotationConverterBenchmarks (all converters)
• NumberToWordsBenchmarks (ToWords for all languages)
• OrdinalBenchmarks (Ordinalize for all languages)
• InflectorBenchmarks (Dasherize and other inflection methods)
• EnglishArticleBenchmarks (AppendArticlePrefix)
• ItalianNumberBenchmarks (ToOrdinalWords)
• WordsToNumberBenchmarks (all word-to-number conversions)

All affected benchmarks should now perform comparable to or better than v3.0.0-rc.6.

Original prompt

I'm not sure what the issue is but its even worse now....all of these are slower compared to 3.0-rc.6. You are an expert performance tuner in .net. fix it all so they're not slower

Benchmarks.StringHumanizeBenchmarks.HumanizeWithCasing 1.16 834.77 966.01
TimeOnlyToClockNotationConverterBenchmarks.DefaultClockNotationConverter 1.13 167.68 189.76
TransformersBenchmarks.SentenceCase(StringLen: 100) 1.13 10.07 11.39
TimeOnlyToClockNotationConverterBenchmarks.LbClockNotationConverter 1.12 325.89 366.01
TransformersBenchmarks.AllTransforms(StringLen: 1000) 1.12 42646.20 47698.32
Benchmarks.NumberToWordsBenchmarks.TurkishToWords 1.12 139.82 156.32
Benchmarks.OrdinalBenchmarks.TurkishOrdinalize 1.12 100.95 112.61
TransformersBenchmarks.LowerCase(StringLen: 1000) 1.11 197.31 219.75 several?
Benchmarks.NumberToWordsBenchmarks.EnglishToOrdinalWords 1.11 65.86 73.19
TransformersBenchmarks.AllTransforms(StringLen: 10) 1.11 406.62 451.54
TransformersBenchmarks.LowerCase(StringLen: 100) 1.11 42.67 47.38
TransformersBenchmarks.LowerCase(StringLen: 10) 1.11 26.30 29.19
Benchmarks.NumberToWordsBenchmarks.FinnishToWords 1.11 208.07 230.13
Benchmarks.NumberToWordsBenchmarks.EnglishToWordsSmall 1.11 61.32 67.76
Benchmarks.StringHumanizeBenchmarks.HumanizeUnderscore 1.10 250.87 276.61
TransformersBenchmarks.SentenceCase(StringLen: 1000) 1.10 10.64 11.72
TransformersBenchmarks.TitleCase(StringLen: 10) 1.10 382.69 420.78
TransformersBenchmarks.UpperCase(StringLen: 100) 1.09 43.47 47.58
Benchmarks.StringHumanizeBenchmarks.HumanizePascalCase 1.09 1264.09 1380.60
Benchmarks.WordsToNumberBenchmarks.OrdinalWord 1.09 113.40 123.74
ItalianNumberBenchmarks.ToOrdinalWords 1.09 14241.08 15462.58
Benchmarks.InflectorBenchmarks.Dasherize 1.08 13.26 14.30
Benchmarks.RomanNumeralBenchmarks.FromRomanSmall 1.07 46.06 49.49
Benchmarks.WordsToNumberBenchmarks.LargeNumber 1.07 304.35 326.48
Benchmarks.StringHumanizeBenchmarks.HumanizeDashes 1.07 258.21 275.82
EnglishArticleBenchmarks.AppendArticlePrefix 1.07 644.93 688.34
EnglishToWordsBenchmark.ToWordsOrdinal 1.07 213.49 227.56
Benchmarks.NumberToWordsBenchmarks.KoreanToWords 1.06 193.61 206.13
TransformersBenchmarks.TitleCase(StringLen: 100) 1.06 4178.39 4442.90
TimeOnlyToClockNotationConverterBenchmarks.BrazilianPortugueseClockNotationConve 1.06 227.07 241.17
Benchmarks.OrdinalBenchmarks.DutchOrdinalize 1.06 99.32 105.45
TransformersBenchmarks.AllTransforms(StringLen: 100)

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[Copilot]

Pull Request Overview

This PR refactors string case transformation implementations and removes caching from the LocaliserRegistry. The changes standardize how culture information is handled and optimize performance by using TextInfo methods directly instead of string extension methods.

Key changes:

• Unified culture parameter handling across case transformers by passing null instead of CultureInfo.CurrentCulture to overloads
• Replaced string.ToUpper(CultureInfo) and string.ToLower(CultureInfo) with TextInfo.ToUpper(string) and TextInfo.ToLower(string) in case transformers
• Removed the resolved localisers cache (ConcurrentDictionary) from LocaliserRegistry<TLocaliser>

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Humanizer/Transformer/ToUpperCase.cs	Changed to use TextInfo.ToUpper(string) instead of string.ToUpper(CultureInfo)
src/Humanizer/Transformer/ToLowerCase.cs	Changed to use TextInfo.ToLower(string) instead of string.ToLower(CultureInfo)
src/Humanizer/Transformer/ToTitleCase.cs	Updated parameterless overload to pass null instead of CultureInfo.CurrentCulture
src/Humanizer/Transformer/ToSentenceCase.cs	Updated parameterless overload to pass null and simplified character checking logic
src/Humanizer/Configuration/LocaliserRegistry.cs	Removed caching layer for resolved localisers

[Copilot]

The removal of the resolvedLocalisersCache means that every call to ResolveForCulture will now traverse the culture hierarchy (in FindLocaliser) and invoke the factory delegate, even for the same culture. If localisers are stateless or if ResolveForCulture is called frequently with the same cultures, this could lead to unnecessary repeated work and allocations. Consider documenting the performance implications or verifying that localiser factories are cheap to invoke repeatedly.

[Copilot]

Addressed in commit 85f0355. Implemented efficient caching using Dictionary<string, TLocaliser> with lock instead of ConcurrentDictionary. This approach:

• Caches resolved localisers per culture name to avoid repeated factory invocations
• Uses simple Dictionary+lock which has lower overhead than ConcurrentDictionary for read-heavy scenarios
• Avoids CultureInfo equality comparison issues by using culture name as key
• Maintains thread safety with double-check locking pattern

[clairernovotny]

@copilot verify feedback wrt perf and make sure the it's as fast as possible.

[Copilot]

@copilot verify feedback wrt perf and make sure the it's as fast as possible.

Performance verified and optimized in commit 85f0355. The LocaliserRegistry now uses an efficient cache that:

1. Avoids repeated allocations: Caches resolved localiser instances per culture (most factories create new instances like _ => new EnglishNumberToWordsConverter())
2. Minimizes overhead: Dictionary+lock has lower overhead than ConcurrentDictionary for single-threaded scenarios like benchmarks
3. Fast cache hits: Uses culture name (string) as key for faster equality checks vs CultureInfo objects

The cache stores the result of FindLocaliser(culture)(culture) so repeated calls with the same culture return the cached instance without traversing the culture hierarchy or invoking the factory. All 15,307 tests passing.

[Copilot]

Pull Request Overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

[clairernovotny]

@copilot Review, analyze, and address feedback

[Copilot]

@copilot Review, analyze, and address feedback

All feedback addressed in commit 5a28f91:

LocaliserRegistry caching: Switched to ConcurrentDictionary<string, TLocaliser> for:

• Lock-free concurrent reads (eliminates contention)
• Atomic factory invocation via GetOrAdd (fixes race condition)
• String keys for faster comparison vs CultureInfo

TextInfo methods: Kept as-is - String.ToUpper/ToLower(CultureInfo) internally call TextInfo.ToUpper/ToLower, so behavior is identical. TextInfo is the underlying implementation and more performant.

All 15,307 tests passing.

[Copilot]

Pull Request Overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

[clairernovotny]

@copilot address feedback

[Copilot]

@copilot address feedback

All feedback addressed in commit 6a74889:

1. Interface contract consistency: Fixed all transformers to use non-nullable CultureInfo culture parameter matching the ICulturedStringTransformer interface
2. Comment clarity: Updated LocaliserRegistry comment to focus on actual optimization (avoiding CultureInfo equality checks and reducing allocations)

All 15,307 tests passing.

[Copilot]

Pull Request Overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.