Oh I actually had some editing mistake, I meant to say that also Rust has restrict by default, by virtue of all references being unique xor readonly.

As I understand it, the Fortran compiler just expects your code to respect the "restrictness", it doesn't enforce it.

So that's where the intent system comes in (an argument can be in/out/inout) as well as the built-in array sizes, because it allows you to express what you want and then the compiler will enforce it. In Fortran you kinda have to work hard to invade the memory of one array from another, as they are allocated as distinct memory regions with their own space from the beginning. Pointer math is almost never necessary. Because there is built-in support for multidim arrays and array lengths, arrays are internally anyways built as flat memory regions, the same way you'd do it in C-arrays for good performance (i.e. cache locality), but with simple indices to address them. This then makes it unnecessary to treat memory as aliased by default.

Honestly, I still don't get why people have built up all these complex numerics frameworks in C and C++. Just use Fortran - it's built for exactly this usecase, and scientists will still be able to read your code without a CS degree. In fact, they'll probably be the ones writing it in the first place.