[API Proposal]: ReadOnlySpan<char>.StartsWithAny(SearchValues<string>) and ReadOnlySpan<char>.EndsWithAny(SearchValues<string>)

[silkfire]

Background and motivation

There currently doesn't seem to be a means of checking whether the beginning or the end of a string equals to any of the values contained in a specified set of values in an optimized way using SearchValues<string> that was introduced in .NET 9. There are other specialized extension APIs involving ReadOnlySpan<char> and SearchValues<string> that were recently added (e.g. IndexOfAny<T>(ReadOnlySpan<char>, SearchValues<string>), ContainsAny(ReadOnlySpan<char>, SearchValues<string>) et al.) but this particular API seems to be missing.

One use case could be if you need to efficiently check whether a string starts with any one of a particular set of prefixes in order to determine whether your application code supports or handles that particular item.

See also #94155.

API Proposal

namespace System;

public static class MemoryExtensions
{
    // Proposed
    public static bool StartsWithAny(this System.ReadOnlySpan<char> span, System.Buffers.SearchValues<string> values);
    public static bool EndsWithAny(this System.ReadOnlySpan<char> span, System.Buffers.SearchValues<string> values);
}

API Usage

var searchValues = SearchValues.Create(new[] { "P1", A99", "B44" }.AsSpan(), StringComparison.Ordinal);

var isSupported = "testValue".StartsWithAny(searchValues);
var isSupported2 = "testValue".EndsWithAny(searchValues);

Alternative Designs

N/A

Risks

N/A

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[MihaZupan]

What sort of use cases do you have for EndsWithAny (note that we also didn't expose a LastIndexOfAny for SearchValues<string>)?

[silkfire]

Good question; I actually wasn't aware of that. I assume StartsWithAny would be more common (and therefore more useful) than EndsWithAny so including the latter one would only be to make the API complete.

[jkoritzinsky]

Re StartsWithAny, I have a use case in #104999 where I'd love to use it.

I don't currently have a use case for EndsWithAny though.

[MihaZupan]

As a workaround, you can use text.IndexOfAny(values) == 0, which would give you the same answer.
Depending on your inputs, that could be more expensive than intended though (long haystack with no matches).

[jeffhandley]

Assigned to @krwq for triage and consultation with @MihaZupan and @stephentoub.