Regex: How to get the value of a capture group when the input is a ReadOnlySpan<char>?

[elgonzo]

I struggle with the ReadOnlySpan<char>-based API for System.Text.RegularExpressions.Regex.

To illustrate my problem, lets imagine this simple task: For the given input string:

ReadOnlySpan<char> input = "12a34b567c890a123c45b678c90";

get the integer values in a(\d+)b(\d+)c and ignore the rest. (The example input is a sequence of numbers delimited by specific word identifiers, with the identifiers represented by a single letter here to keep the example simple and readable.)

With the string-based Regex.Match API that's returning a Match instance, solving the task is a walk in the park. But i don't have a string. I have a ReadOnlySpan<char>. And Regex.EnumerateMatches isn't up for the task -- it only gives me the start index and length of the match for the entire a(\d+)b(\d)c pattern but not for the capture groups.

So, now what? Is the only way forward (with respect to using Regex) to turn the ReadOnlySpan<char> into a string, or is there a better solution hidden from my eyes?

(P.S.: I am not interested in workarounds like employing a sequence of multiple regex pattern matches that break down the input into the parts of interest, and/or copious amounts of look-ahead and look-behind assertions. Because such an approach becomes quickly impractical and error-prone not only from a code maintenance view but especially if the regex patterns need to be configurable outside of the code (for example through a configuration/INI file).

[stephentoub]

turn the ReadOnlySpan into a string

Yes. Span-based input that also supports full reporting of captures is covered by #73223.