And indeed, it's the representation Rust uses. When you have the type Option<T>, if Rust knows that a value of type T can never be zero (as is the case with pointer types), then the compiler uses zero as the machine-level representation for None, which indicates the absence of a value. I get into that a few paragraphs later.

What's important is that you can't use a value of type Option<T> as if it were T; you have to check it first. This is helpful for non-pointer types as well; I include an example of that.