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Easy to say abstractly, but harder to specify exactly which features you would take out. Practical memory safety without GC requires quite a few moving parts.

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@peterbourgon

Jul 15, 2019

it feels like there’s a smaller language hiding in Rust that’s half as powerful at the edges but 10-50x easier to read, write, and maintain

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This isn't a Rust subset, but if I were doing memory-safety for a compiled lang, I'd consider making mutability and ability to hold reference/pointer to objects mutually exclusive. Ref tracking then becomes easy without heavy runtime machinery.

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Support for mutable references definitely makes it harder to design a safe language. However, Rust doesn't need any runtime machinery to support either mutable or immutable references. It deals with it by statically preventing the mutable references from overlapping with others.

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Taking an immutable reference prevents modifying the object and taking a mutable reference prevents getting any usable overlapping references. It's definitely very restrictive, and there are alternatives to this design. Rust has Cell and RefCell as library-based alternatives.

4:10 PM · Jul 15, 2019Twitter Web Client

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There are clearly ways of doing it differently than Rust though. Many of those different approaches were considered as part of the design. There were a lot of experiments with different approaches and it ended up with the model it did largely due to practical research efforts.

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For example, it could have had language support for the concept behind the Cell type in the standard library. It would be a lot more flexible as a language implementation rather than built as a crippled library type. I don't think it would be worth having another reference type.