[ithkuil]

The semantics change. You're now returning a pointer to the actual Rule in the Ruleset, while before you'd be returning a pointer to copy of the Rule.

The optimization would only work if you had a way to tell the compiler that some values are constant/immutable.

[ithkuil]

BTW; I'm using both Go and Rust lately.

In Rust you can write a function that returns the pointer of one element of a slice. You can also write a function that returns the pointer to a heap-allocated copy of an element of the slice. The two functions would have different signatures.

The compiler would also prevent mutation of the slice as long as there are any references to individual elements of the slice being passed around.

[ok123456]

>In Rust you can write a function that returns the pointer of one element of a slice.

Have fun fighting the borrow checker on that one.

[oconnor663]

It's not always so bad :) https://play.rust-lang.org/?version=stable&mode=debug&editio...

[ok123456]

Now try to actually do that in a larger program without static lifetimes...

[piperswe]

It shouldn't be too bad as long as you keep in mind that it is a reference to an item in that slice, so whatever that slice is pointing to needs to stick around as long as you're using elements from it. I don't often encounter borrow checker issues anymore, because once you program Rust long enough you know what things need to live for what lifetimes, and you architect your "larger programs" around that.

[ithkuil]

Yes and that's the whole point!

The borrow checker ensures that you either do it right or you find another way that is safe.

For example it may be totally fine to help allocate a result, not all programs need to be optimized to the bone. Just return a boxed value. If you need to share it, wrap it in an Rc or Arc.

One problem I see with it is that rust chooses to make the most efficient way of programming also the most "simple looking", and so it lines up incentives in such a way that people will unnecessarily try to avoid using an extra Arc just because it looks like unnecessary clutter.

When you learn to embrace your boxing you'll learn that the borrow checker is not your enemy.

[lanstin]

Oh yeah. Too bad. Just ran the escape to heap analysis on my current project, not looking too promising. Mostly it is allocating structure and saving them in a huge in memory hash.