I thought the name apply_by_to_key would be more descriptive. When this new keyword is set to false, by is still applied to the vector being searched but not the key. However, perhaps apply_by is better for other reasons. Could I request that you re-post your suggestion in the discussion of the pull request?
Right now the pull request is failing all CI checks. If I understand the CI log correctly, the PR is failing because Val is undefined. This didn’t happen when I built it locally, so I will have to look into what is causing the problem.