These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.00 s (backtrack: 0/20).

[ebuild  N     ] dev-cpp/functional-plus-0.2.22::gentoo  USE="-test" 277 KiB
[ebuild  N     ] dev-cpp/nlohmann_json-3.12.0-r1::gentoo  USE="-test" 9452 KiB
[ebuild  N     ] dev-cpp/frugally-deep-0.15.30::gentoo  208 KiB

Total: 3 packages (3 new), Size of downloads: 9936 KiB