[API] Avoid SpanAttributes array enumeration

[thomhurst]

Changes

Use ReadOnlySpan<T> enumeration when the existing SpanAttributes
IEnumerable<T> constructor receives an array. Arbitrary enumerable inputs
retain the existing path, and public API remains unchanged.

An IReadOnlyList<T> indexed path was also tested. It had no allocation benefit
for List<T> on .NET 10 and mixed timing results, so it is not included.

Benchmark

A task-scoped BenchmarkDotNet benchmark constructed SpanAttributes from a
pre-created array containing 1, 5, or 20 attributes. It was run before and after
this change using BenchmarkDotNet 0.15.8 on .NET 10.0.11, Windows 11, Intel Core
i7-12700K.

Items	Before	After	Change	Allocated before	Allocated after
1	25.12 ns	22.84 ns	-9.1%	200 B	168 B
5	89.52 ns	65.42 ns	-26.9%	352 B	320 B
20	413.17 ns	407.74 ns	-1.3%	1,168 B	1,136 B

The array path removes 32 B per construction at every tested size.

Benchmark method:

[Benchmark]
public SpanAttributes FromArray()
    => new(this.array);

array was initialized in GlobalSetup; [MemoryDiagnoser] was enabled and
ItemCount used [Params(1, 5, 20)].

Merge requirement checklist

• CONTRIBUTING guidelines followed
• All 6 SpanAttributesTests pass
• Appropriate CHANGELOG.md files updated for non-trivial changes
• No public API changes

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Pull request dashboard status

Merged · refreshed 2026-09-08 10:14 UTC

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.68%. Comparing base (a2b9672) to head (4fd439b).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7698      +/-   ##
==========================================
- Coverage   91.69%   91.68%   -0.01%     
==========================================
  Files         333      333              
  Lines       18287    18290       +3     
==========================================
+ Hits        16769    16770       +1     
- Misses       1518     1520       +2     

Flag	Coverage Δ
unittests-Project-Experimental	91.70% <100.00%> (-0.10%)	⬇️
unittests-Project-Stable	91.79% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/OpenTelemetry.Api/Trace/SpanAttributes.cs	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

[martincostello]

Could you add/update some tests for the missing patch coverage please?

[thomhurst]

Woops sorry @martincostello I missed these notifications. Looks like you're on it?

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Thank you for your contribution @thomhurst! 🎉 We would like to hear from you about your experience contributing to OpenTelemetry by taking a few minutes to fill out this survey.