dotnet/runtime

TakeLast Performance Improvement suggestion

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#118,312 opened on Aug 3, 2025

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 (3 comments) (0 reactions) (0 assignees)C# (17,886 stars) (5,445 forks)batch import
area-System.Linqhelp wantedtenet-performance

Description

TakeRangeFromEndIterator uses a regular Queue <T>when IsStartIndexFromEnd, but this process can be done without intervening yields, allowing optimization using ArrayPool and Span.

https://github.com/dotnet/runtime/blob/3f25a276772b8d0e54452321e7525b7a176aa4a7/src/libraries/System.Linq/src/System/Linq/Take.cs#L111C13-L154C18

Below is the PR I did on ZLinq. https://github.com/Cysharp/ZLinq/pull/207/files Unlike ZLinq, a ToArray is required at the end of the queueing for Linq, but it will be similar.

Contributor guide

Tech stack
csharp
Domain
backend
Issue type
performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
C#LINQArrayPoolSpan<T>
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Examine the current implementation of TakeRangeFromEndIterator in Take.cs (line 111). Review the linked PR in ZLinq (https://github.com/Cysharp/ZLinq/pull/207) for optimization patterns using ArrayPool and Span. Investigate whether ToArray is necessary after queueing and if the same approach can be applied without breaking changes. Consider performance benchmarks and memory allocation trade offs.