Yes, its somewhat similar, monomorphic specialization.

I am sure it has some limitations, but it is pretty powerful, it can even do things C++ can't, like have a type error in a branch that in the current specialization is never executed doesn't count as a type error :)

There's no FPL style pattern matching. It can do a switch case on types (the various subclasses of a base class) but only 1 level, i.e. can't match against type of members. That could still be added, just personally rarely have use for it.