3 ms·

The key is that Rust lets you define safe interfaces, so you can separate your data races and union juggling, which need to be unsafe, from your business logic,

The key is that Rust lets you define safe interfaces, so you can separate your data races and union juggling, which need to be unsafe, from your business logic, which basically never needs to be unsafe.

nyanpasu64 4y ago
"Object graph" architectures are common in C++ and sometimes necessary in Rust for business logic, when building GUI applications or emulators. But Rust doesn't allow mutating through a &/Rc, and throws a compile error if you create multiple &mut, and the workarounds are unreasonably boilerplate-heavy and RefCell carries runtime overhead, whereas C++ doesn't get in the way of making your code work. I've put together a playground at https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=3b5066c3f091b34b981d7d0ca8748c4d https://play.rust-lang.org/?version=stable&mode=debug&editio.... It's not just dereferencing invalid */& that's illegal in Rust, but constructing and dereferencing valid &/&mut in ways that don't respect tree-shaped mutability. Rust's pointer aliasing rules invalidate otherwise-correct code, placing roadblocks in the way of writing correct code. There's so much creation of &mut (which invalidates aliasing pointers for the duration of the &mut, and invalidates sibling &mut and all pointers constructed from them), that's so implicit I don't know what's legal and what's not by auditing code. (Box<T> used to also invalidate aliasing pointers, but this may be changed. The current plan for enabling self-reference is Pin<&mut T>, but the exact semantics for how and when putting a &mut T in a wrapper struct makes it not invalidate self-reference and incoming pointers, is still not specified.) (I've elaborated further at https://news.ycombinator.com/item?id=33658253 https://news.ycombinator.com/item?id=33658253.)
- zozbot234 4y ago
  You can use UnsafeCell https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html if you commit to manually enforcing RefCell's borrowing rules.

nyanpasu64 4y ago

"Object graph" architectures are common in C++ and sometimes necessary in Rust for business logic, when building GUI applications or emulators. But Rust doesn't allow mutating through a &/Rc, and throws a compile error if you create multiple &mut, and the workarounds are unreasonably boilerplate-heavy and RefCell carries runtime overhead, whereas C++ doesn't get in the way of making your code work. I've put together a playground at https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=3b5066c3f091b34b981d7d0ca8748c4d https://play.rust-lang.org/?version=stable&mode=debug&editio.... It's not just dereferencing invalid */& that's illegal in Rust, but constructing and dereferencing valid &/&mut in ways that don't respect tree-shaped mutability. Rust's pointer aliasing rules invalidate otherwise-correct code, placing roadblocks in the way of writing correct code. There's so much creation of &mut (which invalidates aliasing pointers for the duration of the &mut, and invalidates sibling &mut and all pointers constructed from them), that's so implicit I don't know what's legal and what's not by auditing code. (Box<T> used to also invalidate aliasing pointers, but this may be changed. The current plan for enabling self-reference is Pin<&mut T>, but the exact semantics for how and when putting a &mut T in a wrapper struct makes it not invalidate self-reference and incoming pointers, is still not specified.) (I've elaborated further at https://news.ycombinator.com/item?id=33658253 https://news.ycombinator.com/item?id=33658253.)

zozbot234 4y ago
You can use UnsafeCell https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html if you commit to manually enforcing RefCell's borrowing rules.