Span.StartsWith(ReadOnlySpan<T>|ReadOnlySpan<byte>)

[ahsonkhan]

1. Is StartsWith in the right place? i.e. on Span or extension methods
2. Do we have the right StartsWith, i.e. over T or over byte?
3. Is it efficiently implemented?
4. Should StartsWith have an overload that takes an index?

[jkotas]

Is it efficiently implemented?

It is not because of it depends on SequenceEquals in corefx that is not very efficient. Making Starts with efficient is really about making SequenceEquals efficient.

Should StartsWith have an overload that takes an index?

I do not think so (at least - not for performance reasons).

[davidfowl]

Do we even need StartsWith? Is there a T[] equivalent?

[ahsonkhan]

StartsWith was added as part of dotnet/corefx#17322 (API reviewed here https://github.com/dotnet/corefx/issues/17414)

1. It is an extension method on Span
2. There are overloads for byte and T
3. SequenceEqual has been improved using vectors (Span performance improvements corefx#17029)
4. No, as per @jkotas comments.

Hence, closing.