MRI has more primitives of sort, but they're an implementation detail. Ruby itself conceptually only have objects.
MRI however implements some of them (integers, floats, symbols, true, false, nil, I might have forgotten one or two) using type tagged values instead of pointers to objects.
Type-tagging is easier to make fast for a highly gc'd dynamic language, as it reduces gc pressure substantially to not have to allocate lots of small objects without massive amounts of complex optimisations.
