Replacing string with StringSegment or ReadOnlySpan<char>.

[electricessence]

I've been noticing some places where it seems like StringSegment or ReadOnlySpan<char> would be much better suited for either parameters or return types.

One example I'd like to ask about is IConfigurationSection https://github.com/dotnet/runtime/blob/main/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationSection.cs

Seems like it could be beneficial to use something like StringSegment for .Key or .Path.
I can imagine this as a design decision for simplicity, but it seems like a potential memory benefit would be to use something other than potential string portions of the original string key path.

Just curious what people's thoughts are if any about this with something like IConfigurationSection or any other APIs/Classes where using StringSegment could be better.

[huoyaoyuan]

It depends on your use pattern. If the string is extracted from a long text, using StringSegment will keep the whole original text in memory.

Generally, the short the string lives, it's more beneficial to use span instead of copying.

[electricessence]

Yes. Agreed. I suggest StringSegment as an alternative to ReadOnlySpan<char> for the exact reason that in some cases, you will have the original string retained, like the path/key in a dictionary where you only need a 'segment' of that string to identify where you are in the config tree, etc. I like StringSegment's implicit conversion for parameters since you could reuse a Subsegment as that param. There's also the obvious downsides of spans as they can't be used with certain scopes or as type params.

[Joe4evr]

Changing return/parameter types on shipped APIs is an unacceptable breaking change.

[electricessence]

Yes of course. But we've seen interesting augmentations like .ValueSpan exposed in regex captures to allow for better memory use. You wouldn't change the original API, unless it was 100% compatible, like using StringSegment as a param type as it implicitly converts. What I'm suggesting could easily not be worth it. I'm just curious what people think.