Memory regions

language design Unsafe Code Guidelines
1

Is there a mechanism by which one can limit pointers to a specific region in memory?

We cannot afaik forbid borrows from pointing to anywhere in memory. We could maybe limit ourselves to 'static types, but this does not prevent &'static borrows.

We could've an Allocator which only created pointers into the target region, but we cannot necessarily preclude a user defined type using a different Allocator internally.

You'd just want an unsafe trait which made these promises I guess? I'm wondering specifically about mmapped files which one always mmaps into the same memory region, and contain internal owned pointers, but not necessarily internal borrows.

2

What do you mean by "limit"? What are you hoping to do with this limitation? How do you want to consume such pointers?

3

Ideally I'd want a Box<T,MMaped<MyRegion>>, Vec<T,MMaped<MyRegion>> which demands T: InMMap<MyRegion> and then T: InMMap<MyRegion> says any pointer P obtained from T satisfies P: InMMap<MyRegion>.

We probably cannot really enforce something like this, not without doing this check in code outside rustc, maybe some proc macro doing the unsafe impl<..> InMMap<MyRegion> for .. bits. It's useful because it lets you have owned pointers within an mmapped file, not portable but very fast.