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Rust is a unique language in that it deallocates memory on the heap without requiring the writer to call free, while at the same time having no need for a g

Rust is a unique language in that it deallocates memory on the heap without requiring the writer to call free, while at the same time having no need for a garbage collector. Someone correct me if I'm wrong but surely this is not unique - don't Objective C and Swift have automatic reference counting which accomplishes much the same thing?

Manishearth 11y ago
Lots of people consider refcounting as "garbage collection". Not everyone, but many people.
Nyetan 11y ago
Intersection ARC, Lifetimes: * Not having to worry about trivial memory/resource allocations ARC - Lifetimes: * Can blow up hilariously with refcount cycles * Incurs a runtime overhead Lifetimes - ARC: * For the subset of allocation patterns it handles, it does so with zero runtime overhead (i.e. invalid programs do not compile, invalid = leaks memory) * Use extends beyond just memory allocation/deallocation (see the concurrency docs [1] for example) (note that Mozilla wrote Rust to help write Servo [2], their prototype highly-parallel browser engine, so this use case was a target from the getgo) * Cannot encode all data structures a GC can (hence why reference counting is part of the stdlib [3]) [1]: https://doc.rust-lang.org/book/concurrency.html https://doc.rust-lang.org/book/concurrency.html [2]: https://github.com/servo/servo https://github.com/servo/servo [3]: https://doc.rust-lang.org/alloc/rc/ https://doc.rust-lang.org/alloc/rc/
- Rusky 11y ago
  > invalid = leaks memory Not quite true- invalid use of lifetimes typically means use-after-free rather than a memory leak (and if you include the standard library, then you can leak memory in safe Rust).
  - tatterdemalion 11y ago
    Its interesting to me how everyone goes to "memory leaks" as their example of memory unsafety, and then if we're talking about Rust we need to clarify that Rust allows leaks (but it makes them hard to do by accident). I guess mnemonically "memory leak" is easier to bring to mind than "dangling pointer" when talking about memory.
    - Gankro 11y ago
      It's also funny because memory leaks literally aren't a memory safety issue. If they were, every garbage collected language would be memory-unsafe.
SamReidHughes 11y ago
Of course it's not unique, that's a core feature of C++.

Manishearth 11y ago

Lots of people consider refcounting as "garbage collection". Not everyone, but many people.

Nyetan 11y ago

Intersection ARC, Lifetimes: * Not having to worry about trivial memory/resource allocations ARC - Lifetimes: * Can blow up hilariously with refcount cycles * Incurs a runtime overhead Lifetimes - ARC: * For the subset of allocation patterns it handles, it does so with zero runtime overhead (i.e. invalid programs do not compile, invalid = leaks memory) * Use extends beyond just memory allocation/deallocation (see the concurrency docs [1] for example) (note that Mozilla wrote Rust to help write Servo [2], their prototype highly-parallel browser engine, so this use case was a target from the getgo) * Cannot encode all data structures a GC can (hence why reference counting is part of the stdlib [3]) [1]: https://doc.rust-lang.org/book/concurrency.html https://doc.rust-lang.org/book/concurrency.html [2]: https://github.com/servo/servo https://github.com/servo/servo [3]: https://doc.rust-lang.org/alloc/rc/ https://doc.rust-lang.org/alloc/rc/

Rusky 11y ago
> invalid = leaks memory Not quite true- invalid use of lifetimes typically means use-after-free rather than a memory leak (and if you include the standard library, then you can leak memory in safe Rust).
- tatterdemalion 11y ago
  Its interesting to me how everyone goes to "memory leaks" as their example of memory unsafety, and then if we're talking about Rust we need to clarify that Rust allows leaks (but it makes them hard to do by accident). I guess mnemonically "memory leak" is easier to bring to mind than "dangling pointer" when talking about memory.
  - Gankro 11y ago
    It's also funny because memory leaks literally aren't a memory safety issue. If they were, every garbage collected language would be memory-unsafe.

SamReidHughes 11y ago

Of course it's not unique, that's a core feature of C++.