X-Git-Url: https://git.ralfj.de/rust-101.git/blobdiff_plain/832768ac8f69b436c1f90ad7a2f01af25091599a..45ec4d50797cdac0edb7c4653e71357fa6ab54a1:/src/part10.rs?ds=sidebyside diff --git a/src/part10.rs b/src/part10.rs index 6969889..b586cd5 100644 --- a/src/part10.rs +++ b/src/part10.rs @@ -9,10 +9,10 @@ use part05::BigInt; //@ our function. In Rust, a natural first attempt to express this is to have a trait for it. // So, let us define a trait that demands that the type provides some method `do_action` on digits. -//@ This immediately raises the question: How do we pass `self` to that function? Owned, shared borrow, -//@ or mutable borrow? The typical strategy to answer this question is to use the strongest +//@ This immediately raises the question: How do we pass `self` to that function? Owned, shared reference, +//@ or mutable reference? The typical strategy to answer this question is to use the strongest //@ type that still works. Certainly, passing `self` in owned form does not work: Then the function -//@ would consume `self`, and we could not call it again, on the second digit. So let's go with a mutable borrow. +//@ would consume `self`, and we could not call it again, on the second digit. So let's go with a mutable reference. trait Action { fn do_action(&mut self, digit: u64); } @@ -21,7 +21,7 @@ trait Action { impl BigInt { fn act_v1(&self, mut a: A) { //@ Remember that the `mut` above is just an annotation to Rust, telling it that we're okay with `a` being mutated. - //@ Calling `do_action` on `a` takes a mutable borrow, so mutation could indeed happen. + //@ Calling `do_action` on `a` takes a mutable reference, so mutation could indeed happen. for digit in self { a.do_action(digit); /*@*/ } @@ -62,7 +62,7 @@ pub fn main() { //@ In general, this is called a *closure*. Closures take some arguments and produce a result, and they have an *environment* //@ they can use, which corresponds to the type `PrintWithString` (or any other type implementing `Action`). Again we have the //@ choice of passing this environment in owned or borrowed form, so there are three traits for closures in Rust: `Fn`-closures -//@ get a shared borrow, `FnMut`-closures get a mutable borrow, and `FnOnce`-closures consume their environment (and can hence +//@ get a shared reference, `FnMut`-closures get a mutable reference, and `FnOnce`-closures consume their environment (and can hence //@ be called only once). The syntax for a closure trait which takes arguments of type `T1`, `T2`, ... and returns something //@ of type `U` is `Fn(T1, T2, ...) -> U`. @@ -94,11 +94,11 @@ pub fn print_with_prefix(b: &BigInt, prefix: String) { // For example, we can use that to count the digits as they are printed. pub fn print_and_count(b: &BigInt) { let mut count: usize = 0; - //@ This time, the environment will contain a field of type `&mut usize`, that will be initialized with a mutable borrow of + //@ This time, the environment will contain a field of type `&mut usize`, that will be initialized with a mutable reference of //@ `count`. The closure, since it mutably borrows its environment, is able to access this field and mutate `count` - //@ through it. Once `act` returns, the closure is destroyed and the borrow of `count` ends. Because closures compile down + //@ through it. Once `act` returns, the closure is destroyed and `count` is no longer borrowed. Because closures compile down //@ to normal types, all the borrow checking continues to work as usually, and we cannot accidentally leak a closure somewhere - //@ that still contains, in its environment, a borrow that has ended. + //@ that still contains, in its environment, a dead reference. b.act(|digit| { println!("{}: {}", count, digit); count = count +1; } ); println!("There are {} digits", count); }