Copy-on-Write Str

Implementing copy-on-write semantics in C++

This medium-difficulty coding problem tests your ability to design and implement a memory-efficient string class using copy-on-write (COW) semantics. It is representative of systems-level interview questions at firms where performance and resource efficiency matter—particularly in contexts where many string instances are created but most remain immutable.

The core challenge is to allow multiple instances to safely share a single underlying buffer for reads, while ensuring that any modification triggers a lazy deep copy before the change is made. Your implementation must balance three competing constraints: minimizing the size footprint of each instance (the class object itself must fit in 16 bytes), avoiding unnecessary allocations and copies, and maintaining constant-time access operations. You'll need to manage reference counting or a similar sharing mechanism without relying on standard library smart pointers.

• Memory layout and pointer indirection patterns
• Lazy copying and write-time allocation decisions
• Reference counting and lifetime management
• Distinction between const and mutable access operators
• Null-termination and C-string compatibility