I agree that passing a reference is not the same thing as passing the actual value. If it were, there would really be no point to references. However, it does contradict affinity. Specifically, the fact that multiple references can be created from the same value, combined with the properties of references, contradicts affinity.
> At its core, "affine" means that the type system has exchange and weakening but not contraction, and that exactly characterizes Rust's type system.
Well, the rust type system certainly does support contraction, as I can use a reference multiple times. So what is that if not contraction? It seems like rust at least does support contraction for references.
But in practice, having absolutely no contraction is not a very useful definition of affine, because no practical programming language would ever satisfy it. It prohibits too much and the language would not even be turing complete. Instead, there is usually an "affine world" and an "exponential world". (Exponential meaning "unrestricted" values that you can do whatever you want with). And the convention is that values can go from the exponential world to the affine world, but not back. So a function taking an affine value can be passed any value, but must use in in an affine way, and meanwhile but a function taking an exponential (unrestricted) value can only be passed exponential and not an affine value.
If you don't believe me, you can try using linear haskell, and notice that a function taking a linear argument can be passed a non-linear argument, but not the other way around.
If you interpret Rust's type system this way, it's natural to interpret references as exponentials. But references have the opposite convention. You can go from owned values to references, but not the other way around, which is precisely the opposite situation as the convention around linear/affine type systems. Because these systems feel very different to use and enforce very different properties, I do think it's important that we have separate names for them rather than referring to both as "affine". And the usual name for the rust-like system is "uniqueness types", see https://docs.idris-lang.org/en/latest/reference/uniqueness-t... or https://en.wikipedia.org/wiki/Uniqueness_type .