you_can::turn_off_the_borrow_checker • Hacker News Board

Re: you_can::turn_off_the_borrow_checker

#11

Post by himata4113 » Mon, May 25, 2026, 1:36 PM UTC

EFLKumo wrote: post #7

though said for education purpose, keep finding these boundary-pushings playful. I can recall early days arrested by "several ways to access private members in C++" lol

I personally hate access controls in general since it always made be release a big sigh as a I was typing .getClass().getMethod()/getField() knowing that it hurts performance.

Re: you_can::turn_off_the_borrow_checker

#12

Post by kibwen » Mon, May 25, 2026, 1:38 PM UTC

codedokode wrote: post #6

Macros can secretly add "unsafe" blocks into the code?

If you're paranoid, you can use the `forbid(unsafe_code)` attribute, which will produce a compiler error when any code in its scope attempts to use `unsafe`, which includes macro expansions.

Re: you_can::turn_off_the_borrow_checker

#13

Post by estebank » Mon, May 25, 2026, 1:58 PM UTC

himata4113 wrote: post #11

EFLKumo wrote: post #7

though said for education purpose, keep finding these boundary-pushings playful. I can recall early days arrested by "several ways to access private members in C++" lol

I personally hate access controls in general since it always made be release a big sigh as a I was typing .getClass().getMethod()/getField() knowing that it hurts performance.

That kind of code doesn't have to hurt performance, as long as monomorphization, inlining or JITting are available to the toolchain. If every single method access is a virtual-table call, then yes, there's an "unnecessary" cost. But you shouldn't be writing high-level looking code in such a language if you care about that level of performance.

Re: you_can::turn_off_the_borrow_checker

#14

Post by estebank » Mon, May 25, 2026, 2:00 PM UTC

mplanchard wrote: post #9

codedokode wrote: post #6

Macros can secretly add "unsafe" blocks into the code?

Macros are just text in, text out, so yep

Rust macros are Token Trees and provide namespace hygiene, so not quite "text in, text out".

Re: you_can::turn_off_the_borrow_checker

#15

Post by himata4113 » Mon, May 25, 2026, 2:02 PM UTC

estebank wrote: post #13

himata4113 wrote: post #11

Earlier quoted context omitted.

I personally hate access controls in general since it always made be release a big sigh as a I was typing .getClass().getMethod()/getField() knowing that it hurts performance.

That kind of code doesn't have to hurt performance, as long as monomorphization, inlining or JITting are available to the toolchain. If every single method access is a virtual-table call, then yes, there's an "unnecessary" cost. But you shouldn't be writing high-level looking code in such a language if you care about that level of performance.

it's more about the fact that the servers are java and invoking a reflection method does have a non-zero cost that isn't substantial but still makes you sigh as you either eat the performance cost or spend 10 minutes creating a patch and recompiling the server.

Re: you_can::turn_off_the_borrow_checker

#16

Post by rurban » Mon, May 25, 2026, 2:04 PM UTC

Even more unsafe rust, great!

Re: you_can::turn_off_the_borrow_checker

#17

Post by tempesttempo86 » Mon, May 25, 2026, 2:18 PM UTC

Arbitrary mention: Crust[0]

[0] https://github.com/tsoding/crust

Re: you_can::turn_off_the_borrow_checker

#18

Post by Pesthuf » Mon, May 25, 2026, 2:20 PM UTC

I wonder if this has any measurable impact on compile times.

Re: you_can::turn_off_the_borrow_checker

#19

Post by 0x1ceb00da » Mon, May 25, 2026, 3:51 PM UTC

estebank wrote: post #14

mplanchard wrote: post #9

Earlier quoted context omitted.

Macros are just text in, text out, so yep

Rust macros are Token Trees and provide namespace hygiene, so not quite "text in, text out".

Token list, not token trees. There are official libraries for parsing token stream as rust code but you can parse it as anything (eg json, html) if you want to.

Re: you_can::turn_off_the_borrow_checker

#20

Post by mplanchard » Mon, May 25, 2026, 4:23 PM UTC

estebank wrote: post #14

mplanchard wrote: post #9

Earlier quoted context omitted.

Macros are just text in, text out, so yep

Rust macros are Token Trees and provide namespace hygiene, so not quite "text in, text out".

You know, I was going to say tokens rather than text, but the AI discourse has me so burnt out on the term that I edited it. Regardless, one can emit unsafe blocks from a macro, provided they are valid tokens.