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[API Proposal]: Add no-allocation span-based methods to StringInfo#125070

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[API Proposal]: Add no-allocation span-based methods to StringInfo#125070
Copilot wants to merge 3 commits intomainfrom
copilot/propose-api-for-issue-123092

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Copilot AI commented Mar 2, 2026 •
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StringInfo lacks allocation-free APIs for counting grapheme clusters and extracting text-element ranges. The existing LengthInTextElements builds a cached int[], and SubstringByTextElements always allocates a string. This prototype implements three new APIs to close these gaps.

New APIs

namespace System.Globalization;

public partial class StringInfo
{
    public static int GetLengthInTextElements(ReadOnlySpan<char> str);
    public static Range? GetRangeByTextElements(ReadOnlySpan<char> str, int startingTextElement, int lengthInTextElements);
    public Range? RangeByTextElements(int startingTextElement, int lengthInTextElements);
}

Contract: GetRangeByTextElements / RangeByTextElements throw ArgumentOutOfRangeException for negative arguments; return null when the requested range extends beyond the end of the string.

Usage

// Zero-allocation length validation
if (StringInfo.GetLengthInTextElements(username) > 20) { ... }

// Slice a span without allocating a substring
Range? r = StringInfo.GetRangeByTextElements(span, 0, 50);
ReadOnlySpan<char> truncated = r.HasValue ? span[r.Value] : span;

// Repeated page-slicing on the same string
StringInfo si = new(longText);
Range? page = si.RangeByTextElements(pageIndex * pageSize, pageSize);

Open questions for API review

  • Range? return vs. bool TryGetRangeByTextElements(…, out Range)
  • Whether explicit string overloads are needed for GetLengthInTextElements
  • Whether a single-arg RangeByTextElements(int startingTextElement) (to end of string) should be added

Prototype commit

1409ae6

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    • Triggering command: /usr/bin/gh gh pr comment 125070 --body-file /tmp/proposal.md n.Metadata/src/System/Reflection/Metadata/Internal/StringHeap.cs n.Metadata/src/System/Reflection/Metadata/Internal/BlobHeap.cs n.Metadata/src/S/home/REDACTED/work/runtime/runtime/.dotnet/dotnet n.Metadata/src/S/home/REDACTED/work/runtime/runtime/.dotnet/sdk/11.0.100-preview.1.261�� n.Metadata/src/S/noautoresponse n.Metadata/src/S/nologo n.Me�� n.Metadata/src/S/nodeReuse:true n.Metadata/src/S/low:false System.Security.Cryptography/src/home/REDACTED/work/runtime/runtime/src/libraries/System.Private.C-t System.Security.git System.Security.push System.Security.-v System.Security.origin (http block)

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ericstj commented Mar 2, 2026

This PR is just testing out the API design skill.

@ericstj ericstj added NO-MERGE The PR is not ready for merge yet (see discussion for detailed reasons) NO-REVIEW Experimental/testing PR, do NOT review it labels Mar 2, 2026
Copilot AI and others added 2 commits March 2, 2026 20:14
@ericstj
Add GetLengthInTextElements, GetRangeByTextElements, and RangeByTextE…
c047d9e 
…lements to StringInfo

Co-authored-by: ericstj <8918108+ericstj@users.noreply.github.com>
@ericstj
Address code review feedback: throw for negative args, add remarks, i…
1409ae6 
…mprove test coverage

Co-authored-by: ericstj <8918108+ericstj@users.noreply.github.com>
Copilot AI changed the title [WIP] Propose API changes for issue 123092 [API Proposal]: Add no-allocation span-based methods to StringInfo Mar 2, 2026
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ericstj commented Mar 2, 2026

Seems like the publishing failed but it updated this PR with the proposal details.

@ericstj ericstj closed this Mar 2, 2026
This was referenced Mar 2, 2026
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area-Infrastructure NO-MERGE The PR is not ready for merge yet (see discussion for detailed reasons) NO-REVIEW Experimental/testing PR, do NOT review it

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