Dynamic dispatch is slow in Julia — slower than C++ virtual methods, because C++ method dispatch only depends on a single object type (this) and hence can use vtable lookup.
High-performance code in Julia always relies on devirtualizing critical code. This also means that you can’t easily write performant geometry code in Julia by having an array of geometric objects of different types and relying on dynamic dispatch to execute different methods (determined at runtime) for different objects — you need to implement a different dispatch strategy.
See also this discussion: Union splitting vs C++