Is there any interest for `std::unique_ptr` analogue with weak-semantic?

[denzor200]

Hi everyone,

I’ve implemented a weak-reference-enabled version of std::unique_ptr, called weakable_unique_ptr. The core idea is to combine the strict ownership semantics of std::unique_ptr with the ability to create non-owning observers (called unique_weak_ptr), without introducing shared ownership or thread-safety overhead.

Key Properties

• Exclusive Ownership: The owned object is destroyed when the weakable_unique_ptr is destroyed (like std::unique_ptr);
• Observation: unique_weak_ptr observers automatically expire when the owned object is destroyed (like std::weak_ptr);
• Less cost: no copy operation for weakable_unique_ptr at all, unique_weak_ptr's reference counter without atomic operations.

Implementation Status
Attached is a working prototype of weakable_unique_ptr and unique_weak_ptr, tested on Godbolt's GCC 15.1.
The current implementation is standalone (no modifications to Boost.SmartPtr library required) and supports:

• Move-only semantics (like std::unique_ptr);
• Safe validity checks via try_get() or expired().

The current implementation doesn't support yet:

• Handling array types;
• Handling deleter as reference;
• EBO for deleter;
• Lazy initalization for control block(BTW do we really need to support it?);
• Type erasing for control block(in order not to pollute binary);
• Construction and assignment from std::unique_ptr;
• operator[] for array types;
• implicit conversion to std::shared_ptr.

Use Case Example

struct Node { 
    boost::weakable_unique_ptr<Node> child; 
    boost::unique_weak_ptr<Node> parent; // Safe back-reference 
}; 

void demo() { 
    auto root = boost::make_weakable_unique<Node>(); 
    auto child = boost::make_weakable_unique<Node>(); 
    child->parent = root; // Safe link 
    root->child = std::move(child); 
} // All auto-destructs, no leaks 

This is useful for:

• Trees/ASTs with parent links.
• GUI hierarchies (e.g., widgets owning children but needing parent access).
• Any graph structure where ownership is linear but observation is needed.

Next Steps
If there’s interest, I’d love to:

1. Polish the code to Boost standards.
2. Add exhaustive tests/docs.
3. Integrate with Boost.SmartPtr library.

Questions for the community:

• Does this align with Boost’s goals?
• Should it live under Boost.SmartPtr library or as a standalone utility?
• Any design concerns?

weakable_unique_ptr
The full snippet to play: https://godbolt.org/z/41535cTvo