}
}
- // We can convert any vector of digits into a number, by removing trailing zeros. The `mut`
- // declaration for `v` here is just like the one in `let mut ...`: We completely own `v`, but Rust
- // still asks us to make our intention of modifying it explicit. This `mut` is *not* part of the
- // type of `from_vec` - the caller has to give up ownership of `v` anyway, so they don't care anymore
- // what you do to it.
+ // We can convert any little-endian vector of digits (i.e., least-significant digit first) into a number,
+ // by removing trailing zeros. The `mut` declaration for `v` here is just like the one in `let mut ...`:
+ // We completely own `v`, but Rust still asks us to make our intention of modifying it explicit. This
+ // `mut` is *not* part of the type of `from_vec` - the caller has to give up ownership of `v` anyway, so
+ // they don't care anymore what you do to it.
//
// **Exercise 05.1**: Implement this function.
//
//@ consumes the vector `v`. The caller hence loses access to its vector. However, there is something
//@ we can do if we don't want that to happen: We can explicitly `clone` the vector,
//@ which means that a full (or *deep*) copy will be performed. Technically,
-//@ `clone` takes a borrowed vector, and returns a fully owned one.
+//@ `clone` takes a borrowed vector in the form of a shared reference, and returns a fully owned one.
fn clone_demo() {
let v = vec![0,1 << 16];
let b1 = BigInt::from_vec((&v).clone());
let b2 = BigInt::from_vec(v);
}
-//@ Rust has special treatment for methods that borrow its `self` argument (like `clone`, or
+//@ Rust has special treatment for methods that borrow their `self` argument (like `clone`, or
//@ like `test_invariant` above): It is not necessary to explicitly borrow the receiver of the
//@ method. Hence you could replace `(&v).clone()` by `v.clone()` above. Just try it!
//@ `#[derive(Clone)]` right before the definition of `SomethingOrNothing`.
// **Exercise 05.2**: Write some more functions on `BigInt`. What about a function that returns the number of
-// digits? The number of non-zero digits? The smallest/largest digit? Of course, these should all just borrow `self`.
+// digits? The number of non-zero digits? The smallest/largest digit? Of course, these should all take `self` as a shared reference (i.e., in borrowed form).
// ## Mutation + aliasing considered harmful (part 2)
-//@ Now that we know how to borrow a part of an `enum` (like `v` above), there's another example for why we
+//@ Now that we know how to create references to contents of an `enum` (like `v` above), there's another example we can look at for why we
//@ have to rule out mutation in the presence of aliasing. First, we define an `enum` that can hold either
//@ a number, or a string.
enum Variant {
Number(i32),
Text(String),
}
-//@ Now consider the following piece of code. Like above, `n` will be a borrow of a part of `var`,
-//@ and since we wrote `ref mut`, the borrow will be mutable. In other words, right after the match, `ptr`
+//@ Now consider the following piece of code. Like above, `n` will be a reference to a part of `var`,
+//@ and since we wrote `ref mut`, the reference will be unique and mutable. In other words, right after the match, `ptr`
//@ points to the number that's stored in `var`, where `var` is a `Number`. Remember that `_` means
//@ "we don't care".
fn work_on_variant(mut var: Variant, text: String) {
//@ I hope this example clarifies why Rust has to rule out mutation in the presence of aliasing *in general*,
//@ not just for the specific case of a buffer being reallocated, and old pointers becoming hence invalid.
-//@ [index](main.html) | [previous](part04.html) | [raw source](https://www.ralfj.de/git/rust-101.git/blob_plain/HEAD:/workspace/src/part05.rs) | [next](part06.html)
+//@ [index](main.html) | [previous](part04.html) | [raw source](workspace/src/part05.rs) | [next](part06.html)
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