> If you want full function? Just don't pass/use anything that's mut. Not quite. There are still mutable globals (they just have to have to have the appropriat

> If you want full function? Just don't pass/use anything that's mut. Not quite. There are still mutable globals (they just have to have to have the appropriate "I'm MT-safe" marker traits); and there's nothing preventing any function from performing any I/O that it desires. Even better, once specialization lands, generic trait-functions will be able to behave differently when called on different types, even if the special behavior isn't valid given only the public type-signature's assumptions.