dotnet/roslyn

Generalize `(CollectionBuilderType<T>)[..readOnlySpan]` optimization to spread operands which are implicitly convertible to `ReadOnlySpan<T>`

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#73,110 opened on Apr 19, 2024

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 (5 comments) (0 reactions) (0 assignees)C# (4,257 forks)batch import
Area-CompilersCode Gen QualityFeature - Collection Expressionshelp wanted

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Description

I would welcome a follow-up PR which also handles cases where the spread operand is implicitly convertible to ReadOnlySpan<T>.

Originally posted by @RikkiGibson in https://github.com/dotnet/roslyn/issues/73102#issuecomment-2067272169

Affected scenarios would include:

Span<int> span = ..;
MyCollectionBuilderType<T> collection = [..span];

// currently:
MyCollectionBuilderType<T> collection = MyCollectionBuilderType.Create((ReadOnlySpan<T>)span.ToArray());

// could change to:
MyCollectionBuilderType<T> collection = MyCollectionBuilderType.Create((ReadOnlySpan<T>)span);

Contributor guide

Research direction
Examine the existing optimization in the Roslyn compiler for collection builder spread with ReadOnlySpan<T> and identify the necessary changes to support implicit conversions. Look at the linked issue for context and trace the compiler code path.
Tech stack
csharp
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50