> The 2000-foot version: Rust structs, enums, and tuples are now automatically smaller in some cases. It's possible for the compiler to work with types whose in-memory field order doesn't match that of your source code.
This would mean (again, as I understand it) that you cannot rely on the order of elements in a tuple, if for example you wanted to pass a `&[(T1,T2)]` to some other code (even other Rust code, but built separately).
Edit: serious follow up: You've been working with Servo, and I'm assuming at various moments you (pl) need to map in shared libraries that Servo wasn't built with (e.g. codecs, whatever). Do you avoid Rust types in these FFI interfaces, do you rewrap everything, or have pervasive repr(C) type analogues instead?
It might be that I'm the only person in the world trying to do Rust-to-Rust FFI, but it feels like (i) it isn't that far from being really tasteful, but (ii) it has a bunch of issues that make it seem that no one has ever tested it (e.g. default allocators being different, weak guarantees about layout).
Isn't std::vector in C++ equally unspecified, though?