> does using the `any` type result in an additional memory lookup if the wrapped type is a sized primitive like an int, or is the value stored directly alongside the type information?
The answer to this question is complicated because it's changed several times.
Prior to Go 1.4, it stored word-sized or smaller values directly without allocation.
Go 1.4 started a big GC rework, part of which required fields not contain possibly-pointer-possibly-other-values. https://github.com/golang/go/issues/8405
Obviously this made people unhappy, so it kicked off several rounds of optimizations to claw back common cases over several versions, the most recent of which was 1.15's introduction of 256 interface constants which are automatically used for any numeric value that fits in a single byte (including booleans). 1.9 also made constant strings preallocate matching constant interfaces if it sees them passed as an interface.
This is also why there's so much benefit to inliner improvements; any inlining improvement translates rapidly into devirtualization improvements.
