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Ownership Types, Views and Type Erasure · 3:44
The Pimpl Idiom
Pimpl (pointer to implementation) moves a class's data members and their includes out of the header and behind a unique_ptr, so the class shrinks to one pointer and clients stop recompiling when its insides change. We watch the client fail to compile because the implicit destructor is generated where Impl is only a name, then fix it by declaring the destructor and moves in the header and defining them in the .cpp, write a deep copy, and see why shared_ptr doesn't have the problem.
You will learn
- Explain what the pimpl idiom hides and why it cuts compile-time dependencies
- Explain why a unique_ptr<Impl> member makes the client fail to compile with an implicit destructor
- Fix it by declaring the destructor and move operations in the header and defining them in the .cpp
- Write a deep copy for a pimpl class, and contrast unique_ptr with shared_ptr pimpl