Add population derived quantity lookup by name in rcpp

[codeafridi]

proof of concept for issue #1291

What is the feature?

This PR adds a small proof of concept for referencing a population derived quantity from R by name. in issue #1291, the main problem is that derived quantities are created during model setup but do not have a consistent R facing access path like parameters do so I focused on a minimal population side example.

How have you implemented the solution?

I added a small registry path in the CatchAtAge Rcpp interface for population derived quantities during model initialization.

The change does the following:

• registers population derived quantities into the existing model setup path
• stores a stable ID for each quantity by name
• exposes an Rcpp method to retrieve the ID from R using the population id and quantity name

For the proof of concept, I used "spawning_biomass".

I also added a focused test in "test-initialize_modules.R" to check that:

• a population derived quantity can be referenced from R by name after model initialization
• an unknown derived quantity returns an error

Does the PR impact any other area of the project, maybe another repo?

No this change is only within FIMS

[kellijohnson-NOAA]

@nathanvaughan-NOAA and @Andrea-Havron-NOAA are you using parts of this PR for your refactor on random effects? If yes, I would like to ensure that @codeafridi gets credit by being a commit author. We can modify this PR if that would be helpful. Please let me know how to proceed. Also, @msupernaw are there parts of the PR that you think should be brought into the codebase?

[nathanvaughan-NOAA]

Not sure at the moment @Kelli Johnson - NOAA Federal ***@***.***> but we will make sure to attribute it correctly if we do. *Nathan R. Vaughan Ph.D.* Research Scientist, Contractor/Affiliate with Vaughan Analytics in support of NOAA Fisheries - Southeast Fisheries Science Center | U.S. Department of Commerce Mobile: (305) 733-6643 www.fisheries.noaa.gov

…

On Tue, May 19, 2026 at 9:49 PM Kelli Johnson ***@***.***> wrote: *kellijohnson-NOAA* left a comment (NOAA-FIMS/FIMS#1357) <#1357 (comment)> @nathanvaughan-NOAA <https://github.com/nathanvaughan-NOAA> and @Andrea-Havron-NOAA <https://github.com/Andrea-Havron-NOAA> are you using parts of this PR for your refactor on random effects? If yes, I would like to ensure that @codeafridi <https://github.com/codeafridi> gets credit by being a commit author. We can modify this PR if that would be helpful. Please let me know how to proceed. Also, @msupernaw <https://github.com/msupernaw> are there parts of the PR that you think should be brought into the codebase? — Reply to this email directly, view it on GitHub <#1357 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AMU2O2VV3RTQRCI2ZP7E6VD43UFLZAVCNFSM6AAAAACW62E3U2VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DIOJTG44DQMJSHE> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you were mentioned.Message ID: ***@***.***>