[imron]

Doesn't help, because you don't necessarily know when the other shared pointer could push something to vector, potentially reallocating the internal array and thereby invalidating any references you had to the contents of the vector.

[hoodedmongoose]

Ah okay - I didn't realize rust was guaranteeing that no one else would _modify_ the vector while an instance of that struct was around. That's pretty cool.

[Manishearth]

Rust follows multiple-readers or single-writer even in single-threaded situations. You can hold multiple immutable references to an object, or a single mutable one.

Initially this gets annoying, but as time passes one realizes how awesome this is. It prevents iterator invalidation (and vector-move-invalidation), for one (it's also necessary to get memory safety for our ADT enums since you can otherwise change the variant and invalidate a reference to its contents). In general you realize that in a large codebase, it's almost as bad as a multithreaded situation -- you don't know what objects are being modified by the methods being called and the code is too large to easily figure it out.

[imron]

It's very cool. Rust guarantees that at any point in time there will only be one part of the code that can modify the contents of some data, and will fail to compile if it detects a situation where this is not the case.