In this code:
fn main() {
let a: Vec<i32> = vec![1,2,3];
let b: &i32 = &a[2];
println!("{a:?}, {b}");
}
Should I think of b as path number 2 in the image below, or paths number 1a and 1b (although in this case I'm unsure how it directs to 1b unless it remembers the offset, somehow ?
If you want to edit the image maybe this can be forked from the source.
The address stored in b points directly to the heap-stored data, which I believe you mean by path 2, right?
You can print the addresses of references using the p formatter by the way:
fn main() {
let a: Vec<i32> = vec![1,2,3];
let b: &i32 = &a[2];
let heap_addr_of_data_of_a: &[i32] = &a;
let addr_of_a_on_stack: &Vec<i32> = &a;
println!("{addr_of_a_on_stack:p}, {heap_addr_of_data_of_a:p}, {b:p}");
}
Neat, thanks, but there are 8 bytes between b and start of data in a?
0x7ffe34f615e8, 0x64ce6f17ab10, 0x64ce6f17ab18
PD: sorry, i thought it was a[1].
from my test this is the same as &a[0], right? It's just handier to me since the type is only &i32 ?
heap_addr_of_data_of_a is a reference to the whole slice on the heap. &a[0] is a reference to the first element of the slice. The latter can only access the first element, the former allows you to inspect all elements of the slice.
In the reply you write:
let heap_addr_of_data_a: &[i32] = &a;
Is that considered the most idiomatic way, or should one use &a[..] ?
Both are semantically equivalent. &a is shorter, but &a[..] a bit more expressive. I wouldn't consider one to be more idiomatic than the other, but that's just my opinion.
Keep in mind that although it only "actually" stores the address of the item when running (with the usual "behaves as-if it follows the rules" caveats once you enable optimizations), the borrow is still a reborrow of the implicit borrow of the Vec when you constructed it, and therefore it prevents simultaneous mutable references to any other item (or the Vec itself, eg with a push()) as a compile-time check.
I don't understand what you mean, sorry. But if you rephrase or add a simple snippet I may.