Comment by masklinn

It didn't, actually. Instead go 1.15 has a static array of the first 256 positive integers, and when it needs to box one for an interface it gets a pointer into that array instead: https://go-review.googlesource.com/c/go/+/216401/4/src/runti...

This array is also used for single-byte strings (which previously had its own array): https://go-review.googlesource.com/c/go/+/221979/3/src/runti...