This week I had a nice discussion on Smart Pointer versus RUST. My takeaways are the following.

Feature	C++ Smart Pointers	Rust Ownership & Borrowing (also has SmartPointer)

Goal

Manage dynamic memory with RAII – “Resource Acquisition Is Initialization”

Ensure memory safety at compile time

Core Concept

Pointer with automatic resource release

Ownership rules enforced by the compiler

Memory Safety

Runtime safety via smart pointers

Compile-time safety via borrow checker

And while programming

Concept	C++	Rust
Unique ownership	std::unique_ptr<T>	Box<T> (heap allocation) + ownership transfer
Shared ownership	std::shared_ptr<T>	Rc<T> (single-threaded), Arc<T> (thread-safe)
Non-owning reference	Raw pointer or std::weak_ptr<T>	&T (immutable borrow), &mut T (mutable borrow)
Null safety	nullptr possible	No null references (Option<T> is used instead)

Code example:

#include <memory>

std::unique_ptr<int> makeInt() {
    return std::make_unique<int>(42);
}

int main() {
    std::unique_ptr<int> ptr = makeInt();
    // *ptr = 10; // OK
}

fn make_int() -> Box<i32> {
    Box::new(42)
}

fn main() {
    let ptr = make_int();
    // *ptr = 10; // OK
}

Same ease of use

Safety considerations

Category	C++	Rust

Dangling pointers

Possible if raw pointers or misused shared_ptr

Prevented by ownership rules

Use-after-free

Possible, unless smart pointers are carefully used

Statistically eliminated by borrow checker

Data races

Possible in multithreaded contexts

Compiler prevents them via aliasing rules

Reference counting

Runtime cost with shared_ptr/weak_ptr

Runtime cost with Rc/Arc, compile-time borrow checks otherwise

Zero-cost abstraction

Not guaranteed

Strong focus on zero-cost abstractions

Reference Cycles

But also consider this nice chapter in the RUST handbook: Reference Cycles Can Leak Memory – The Rust Programming Language

Even though Rust enforces strict memory safety at compile time, reference cycles are still possible when using reference-counted types like Rc<T> or Arc<T>—similar to shared_ptr in C++. This is one of the few scenarios in which Rust can leak memory, albeit safely (i.e., without undefined behavior).

Concept	C++	Rust
Reference cycles	Can occur with std::shared_ptr	Can occur with Rc<T> or Arc<T>
Prevention	Use std::weak_ptr to break cycles	Use Weak<T> to break cycles
Memory leak risk	Yes, if cycles are not broken	Yes, in same cases — logic errors, not unsafe
Runtime check?	No automatic detection	No automatic detection eitherEven though Rust enforces strict memory safety at compile time, reference cycles are still possible when using reference-counted types like Rc<T> or Arc<T>—similar to shared_ptr in C++. This is one of the few scenarios in which Rust can leak memory, albeit safely (i.e., without undefined behavior). Concept C++ Rust Reference cycles Can occur with std::shared_ptr Can occur with Rc<T> or Arc<T> Prevention Use std::weak_ptr to break cycles Use Weak<T> to break cycles Memory leak risk Yes, if cycles are not broken Yes, in same cases — logic errors, not unsafe Runtime check? No automatic detection No automatic detection either