Function as argument

[Benny]

@lrnv

in the OP state of the code, the inner method indeed specializes on the function, but the outer one does not

Correct. Reminds me of a past thread; TLDR yes this exception is unintuitive, but specializing on functions by default improves performance in uncommon situations yet severely bloats compilation of caller chains generally, and chained callee inlining can and often removes the caller chain and nonspecialization issue for argument functions fixed at compile-time e.g. foo(x, y) = map(+, x, y).