isize and usize seem to be more like intptr_t and uintptr_t. To be fair, for a long time it was not very well-defined to which C type they correspond to; I think that was cleared up only recently.

It's also a shame the article uses the self-delusional C++ style of pointer declarators.

Otherwise pretty okay.

They're not great analogs to any of the C types because C and C++ have a different relationship to pointers than Rust does but particularly they are not intptr_t / uintptr_t because those claim that we can intra-convert between these types and pointers.

On a typical PC that doesn't seem like a problem, and it will (at least kinda) work which might give you the false impression it's required to work, which it very much is not in Rust. On CHERI it's obvious why this can't work. CHERI's pointers are 128-bit. Rust does have 128-bit integers, but Rust's isize and usize on CHERI will be 64 bits. Because only half of CHERI's pointer bits are address bits, and Rust told you that isize and usize were big enough for the address not the whole pointer.

Many clever pointer tricks only want to fiddle with the address. For example hiding bit flags in an aligned pointer works, as does hiding the entire value inline in today's enormous pointers (64 bits! Luxury) and using a single bit to mark "not a real pointer". In Rust we do these with the actual raw pointer types, they have methods like any other type, but in C or C++ you need to convert to a pointer-sized integer and then do tricks with the integer or you will write UB.