Status: OUT
Visitor's complete extensibility mechanism requires two independently necessary halves: the dual class hierarchy provides the static architectural framework (orthogonal element and visitor hierarchies enabling structural independence), while double dispatch provides the runtime protocol that makes OCP axis inversion operational and simultaneously eliminates fragile type-switching — together they constitute a unified type-safe extensibility architecture that neither structural separation nor dispatch protocol alone could achieve.
Visitor's dual hierarchy (static architecture) and double dispatch (runtime protocol) are complementary halves of one extensibility mechanism
Depends on (SL): double-dispatch-unifies-type-resolution-across-patterns, visitor-dual-hierarchy-grounds-ocp-inversion-mechanism