Comment by veber-alex
5 hours ago
It's impossible to add a borrow checker to any existing language.
The reason Rust has a working borrow checker is because every part of the language from structs, enum, traits, generics and all the way to the syntax itself has been designed to support lifetimes and borrow checking.
It's is not something you can just tack on to an existing language without fundamentally changing it.
I wouldn't say it's impossible, rather un-ergonomic. TypeScript can add type information to ordinary JavaScript code via JSDoc comments; the result can both be executed as ordinary JavaScript as-is and type-checked with TypeScript. But it's a huge pain to try to write (and maintain) everything that way, it was supported as a hack to help migrate legacy codebases. You could probably take a similar "the lifetimes are embedded in comments" approach with other languages, and the result would be similarly un-ergonomic.
That is possible (clang has experimental lifetime annotations support), but that is not enough to guarantee memory safety.
As a simple example, Zig has no private fields. That makes encapsulating any unsafety impossible.
no. You don't need private fields. All you have to do is analyze the code, harness the compiler to generate a time-dependent data dependency graph, and map allocation/frees/uses, if you can 'color' branches where data are shared you can also track and check to see there isn't an aliasing violation too.
it is easy to patch the zig compiler to enable this this (export the code graph; about 50 LOC). The analysis is much much harder to get right.
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> Zig has no private fields
You may have missed the point here. You could add a comment to the struct field that marks the field as private, and build a TypeScript/JSDoc analogue that analyzes all accesses to the field and fails if it finds accesses from functions that aren't part of the struct that owns the field. You don't even need a comment on the field - you could copy Go's convention, add a comment to the struct definition marking it as "follows Go convention", and then fail any access from outside the struct to a field that starts with a lower-case character.
It doesn't prevent you from ignoring that tool and writing Zig code that imports the struct and accesses the field. It is, of course, not part of the Zig language itself. But if you adopted a tool like that, it would be your responsibility to run it across-the-board and pay attention to the results - same as how it is your responsibility to pay attention to the results if you added those JSDoc comments.
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Exactly.
Every part of the language must support memory safety from first principles.
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C# was already a very mature language when it had referenes and later "ref safety" added to it.
Swift, Linear Haskell, Chapel, Ada/SPARK are all counter examples from such claim.
Also OxCaml, from what I hear.
> It's impossible to add a borrow checker to any existing language.
Why do you say that. Have you tried and failed? It seems to be possible to add a borrow checker to zig, just as you can add MIRI to rust to get extra safety in unsafe blocks.