[HarryCordewener]

Before: splitting a 100-item plain list on spaces took 8.7 µs and 28,336 B, and joining 100 items took 2.7 µs and 8,232 B. Every segment built a run list even with no runs to clip, and Join collected parts and separators into a list, copied it to an array, and copied the parts again in Concat.

After: the same split takes 4.2 µs and 8,752 B (the result array plus one string and one MarkupText per item), and the join takes 1.6 µs and 656 B. Results are the same, runs included.

How: ExtractRange returns a slice with the shared empty run array when the text has no runs. Split counts the delimiters first and fills an exactly sized array. Join with one separator writes the parts and separators straight into the result string and builds runs only if something has them. Concat takes its parts as a span without copying them. Text with runs still goes through the existing run code.

Tests: CsCheck property tests (fixed seed, 5,000 samples each) compare Split, Substring, Concat and Join against copies of the old code on plain and marked input, with empty items, delimiters at both ends, multi-character delimiters and delimiters inside grapheme clusters. An allocation test bounds the plain split and join. All 1,390 tests pass.

The only observable difference: Join(separator, null) now throws ArgumentNullException instead of NullReferenceException.

Patch bump (2.24.3) in CHANGELOG.md. SharpMUSH picks it up with a MarkupStringVersion bump once it is tagged.

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Generated by Claude Code

Summary by CodeRabbit

• Performance Improvements
  • Reduced memory allocations when working with plain text, including substring extraction, splitting, joining, and concatenation.
  • Improved performance when joining collections of text.
• Behavior
  • Text and markup results remain unchanged across these operations.

[coderabbitai]

No actionable comments were generated in the recent review.

Walkthrough

The change updates MarkupText extraction, splitting, concatenation, and joining to reduce allocations. Property-based tests compare text and markup runs with reference implementations, and an allocation test measures plain-text splitting and joining.

Changes

MarkupText text operations

Layer / File(s)	Summary
Plain-text extraction and splitting MarkupString/MarkupText.Operations.cs, MarkupString.Tests/Properties/SplitJoinProperties.cs	ExtractRange skips run clipping when the source has no runs. Split counts delimiter matches, returns the original text when there are none, and sizes the result array to the segment count. Property tests compare split text and runs with reference results.
Span-based concatenation and joining MarkupString/MarkupText.cs, MarkupString.Tests/Properties/SplitJoinProperties.cs, MarkupString.Tests/AllocationTests.cs, CHANGELOG.md	Concat and Join build text and shifted runs from spans, with fast paths for empty and single-item inputs. Enumerable inputs use arrays or list spans when available and materialize other enumerable types. Tests cover overloads, separator call order, and allocation ranges. The changelog records the unreleased entry.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Merge Risk: Minimal · up to 5c1bb

The change reduces intermediate allocations in text operations. No merge-blocking issue was identified.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 42.86% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title names the main change: plain text with no markup is split and joined without the run builder or interleaved copies. The raw summary confirms this. The changes to MarkupText.Operations.cs (Sp…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title names the main change: plain text with no markup is split and joined without the run builder or interleaved copies. The raw summary confirms this. The changes to MarkupText.Operations.cs (Split sizing via delimiter count, ExtractRange short-circuit for run-free text) and MarkupText.cs (span-based Join, Concat without parts array) match the title. The added allocation test and property tests cover the same paths. The title is specific and accurate, though it is long at 81 characters.

Full details: Docstring Coverage

Explanation

Docstring coverage is 42.86% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 14 functions across 4 files. (1 skipped: 1 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

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Commits

Reviewing files that changed from the base of the PR and between 5265e31 and 5c1bb13.

Files selected for processing: 5

• CHANGELOG.md
• MarkupString.Tests/AllocationTests.cs
• MarkupString.Tests/Properties/SplitJoinProperties.cs
• MarkupString/MarkupText.Operations.cs
• MarkupString/MarkupText.cs

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