X-Git-Url: https://git.ralfj.de/rust-101.git/blobdiff_plain/cc2796e7bbd431e53563aef06ede06d69edcede1..0da6e9205576b3191f45190a18d1f7d1e33fb0ea:/src/part09.rs?ds=sidebyside diff --git a/src/part09.rs b/src/part09.rs index 80a9c08..9cad15d 100644 --- a/src/part09.rs +++ b/src/part09.rs @@ -19,6 +19,7 @@ use part05::BigInt; //@ current location. However, it cannot *own* the `BigInt`, because then the number would be gone //@ after iteration! That'd certainly be bad. The only alternative is for the iterator to *borrow* //@ the number, so it takes a reference. + //@ In writing this down, we again have to be explicit about the lifetime of the reference: We //@ can't just have an `Iter`, we must have an `Iter<'a>` that borrows the number for lifetime //@ `'a`. This is our first example of a data-type that's polymorphic in a lifetime, as opposed to @@ -26,7 +27,6 @@ use part05::BigInt; //@ `usize` here is the type of unsigned, pointer-sized numbers. It is typically the type of //@ "lengths of things", in particular, it is the type of the length of a `Vec` and hence the right //@ type to store an offset into the vector of digits. - pub struct Iter<'a> { num: &'a BigInt, idx: usize, // the index of the last number that was returned @@ -118,7 +118,6 @@ fn iter_invalidation_demo() { /*b = b + BigInt::new(1);*/ /* BAD! */ } } - //@ If you enable the bad line, Rust will reject the code. Why? The problem is that we are //@ modifying the number while iterating over it. In other languages, this can have all sorts of //@ effects from inconsistent data or throwing an exception (Java) to bad pointers being @@ -158,7 +157,6 @@ impl<'a> IntoIterator for &'a BigInt { } } // With this in place, you can now replace `b.iter()` in `main` by `&b`. Go ahead and try it!
- //@ Wait, `&b`? Why that? Well, we implemented `IntoIterator` for `&BigInt`. If we are in a place //@ where `b` is already borrowed, we can just do `for digit in b`. If however, we own `b`, we have //@ to create a reference to it. Alternatively, we could implement `IntoIterator` for `BigInt` -