C++ Ownership (Move Semantics & RAII)

Core Question

Who owns this resource, and does it need to move?

In C++, ownership is a discipline, not just a compiler check. You must decide:

• Scope-bound? Use Stack (RAII).
• Exclusive? Use std::unique_ptr.
• Shared? Use std::shared_ptr.
• View? Use T* or T& (non-owning).

Error → Design Question

Thinking Prompt

1. Does it need a heap allocation?
   • No? → Stack value (Rule of Zero).
   • Yes? → std::unique_ptr (Rule of Zero).
   • DO NOT write a destructor unless managing a non-RAII C handle.
2. Is it a Transfer or a Copy?
   • Transfer? → std::move.
   • Copy? → Copy Constructor (or clone() pattern if polymorphic).
3. Is this a View?
   • Yes? → std::string_view, std::span, or const T&.
   • Never pass std::shared_ptr unless transferring shared ownership.

Trace Up / Down

• Trace Up (Diagnosing):
  • Error: "Segfault / Heap Corruption"
  • Ask: Is there a raw pointer (T*) managing a resource?
  • Fix: Wrap in unique_ptr or vector.
• Trace Down (Implementing):
  • Intent: "I want to pass this big object to a function and never see it again."
  • Code: void consume(BigThing t); called with consume(std::move(thing));

Quick Reference