[repo-assist] perf: replace formatObject Array.map+Join with StringBuilder#440
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sergey-tihon merged 2 commits intoMay 17, 2026
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Rewrite formatObject to stream directly into a StringBuilder instead of
- allocating an intermediate string[] via Array.map
- allocating per-property strings via 'p.Name + "=" + s'
- allocating quoted-string via '"\"" + v.ToString() + "\""'
- allocating array result via Array.ofSeq + '[' + Join + ']'
- allocating outer wrapping via '{' + Join(strs) + '}'
All 417 existing unit tests continue to pass.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
This PR optimizes RuntimeHelpers.formatObject in SwaggerProvider.Runtime by switching from building an intermediate string[] (via Array.map + String.Join) to streaming the formatted output directly into a StringBuilder, reducing allocations while preserving the existing formatting contract.
Changes:
- Reimplemented
formatObjectusing a singleStringBuilderpass. - Preserved existing formatting rules:
{Prop=value; ...}, alphabetical property order, quoted strings, bracketed arrays, andnullrendering.
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🤖 This PR was created by Repo Assist, an automated AI assistant.
Summary
Rewrite
RuntimeHelpers.formatObjectto stream output directly into aStringBuilderinstead of building an intermediate array of strings and then joining them.Motivation
The original implementation allocated several short-lived objects per call:
string[]viaArray.mapp.Name + "=" + s(one allocation per property)"\"" + v.ToString() + "\""(two allocations)Array.ofSeq+"[" + String.Join(...) + "]"(extra wrapping alloc)"{" + String.Join(strs) + "}"(extra wrapping alloc)With
StringBuilder, the same output is produced in a single pass with no intermediate string objects.Change
Array.map+String.Joinwith a singleStringBuilderloop informatObject{Prop=value; ...}formatting, alphabetical property order from the cachedgetPropertiesresult, quoted strings, bracketed arrays,nullfor null valuesTest Status
All 417 existing unit tests pass (no new tests needed — existing
FormatObjectTestsmodule already covers the formatting contract).