Compare C++ Virtual Dispatch with CRTP

Explain how C++ virtual functions are commonly implemented and compare runtime polymorphism with the Curiously Recurring Template Pattern. Discuss object layout, dispatch, extensibility, code generation, and when each design is appropriate. ### Constraints & Assumptions - The C++ standard specifies behavior but not one mandatory vtable layout. - The comparison should include separate compilation and heterogeneous collections. - Do not claim that one indirect call is always a meaningful performance problem. ### Clarifying Questions to Ask - Must implementations be selected at runtime or are concrete types known at compile time? - Will objects be handled through one stable ABI across shared-library boundaries? - Is binary size or build time a material constraint? ### What a Strong Answer Covers - A qualified description of vptrs, vtables, overrides, and dynamic dispatch. - Virtual destructors and the danger of deleting through a base without one. - CRTP static dispatch and compile-time interface expectations. - Trade-offs involving runtime flexibility, inlining, code size, diagnostics, and ABI. - A requirement-based choice plus measurement rather than dogma. ### Follow-up Questions - How can devirtualization remove the indirect call? - Can CRTP store unrelated derived objects in one container without another abstraction? - When would type erasure be a better compromise?