[steveklabnik]

> both have the same ABI (just pointers)

This is not actually true, but it's close enough for your purposes here.

But just to be clear about it, see stuff like this: https://stackoverflow.com/questions/58339165/why-can-a-t-be-...

[fathyb]

Another reason it is not true: Rust has fat pointers, eg. `std::unique_ptr<const uint8[]>` and `Box<[u8]>` both contain the same allocation data, but `Box` will be 128-bit on 64-bit systems.

[HarHarVeryFunny]

What's the utility of having a 128-bit pointer on a 64-bit system ?

[fathyb]

`Box<[u8]>` stores the pointer and its length (2 x size_t), `std::unique_ptr<const uint8_t[]>` only stores the pointer.

That's for slices, for dynamically sized types (eg. `Box<dyn ToString>`) it contains a pointer to the virtual table.

https://doc.rust-lang.org/nomicon/exotic-sizes.html

[bitcharmer]

Where can I find details like this about Rust?

[fathyb]

The Rustonomicon is a good start, on fat pointers: https://doc.rust-lang.org/nomicon/exotic-sizes.html

> Because they lack a statically known size, these types can only exist behind a pointer. Any pointer to a DST consequently becomes a wide pointer consisting of the pointer and the information that "completes" them (more on this below).