> Rust's shared XOR mutable references […] makes linearity nearly useless or inevitably creates a parallel, incomplete universe of functions that also work on linear values.
Yup. Rust can't abstract over mutability. For owned values, it defaults to exclusive ownership, and needs explicit Rc<T> and clone() to share them. For references, in practice it requires making separate `foo()` and `foo_mut()` functions for each type of the loan.
Even though this sounds horribly clunky, it works okay in practice. Ability to temporarily borrow exclusively owned objects as either shared or exclusive-mutable adds enough flexibility.
Rust is known for being difficult, but I think a lot of that is due to lack of GC. Rust can't make any reference live longer, and programmers have to manually get scopes of loans right, or manually use Rc<RefCell> to have a mini DIY GC. Perhaps a shared XOR mutable with a GC could be the best of both?
Yup. Rust can't abstract over mutability. For owned values, it defaults to exclusive ownership, and needs explicit Rc<T> and clone() to share them. For references, in practice it requires making separate `foo()` and `foo_mut()` functions for each type of the loan.
Even though this sounds horribly clunky, it works okay in practice. Ability to temporarily borrow exclusively owned objects as either shared or exclusive-mutable adds enough flexibility.
Rust is known for being difficult, but I think a lot of that is due to lack of GC. Rust can't make any reference live longer, and programmers have to manually get scopes of loans right, or manually use Rc<RefCell> to have a mini DIY GC. Perhaps a shared XOR mutable with a GC could be the best of both?