// Rust-101, Part 10: Closures
// ===========================
-use std::io::prelude::*;
-use std::{fmt,io};
+use std::fmt;
use part05::BigInt;
//@ Assume we want to write a function that does *something* on, say, every digit of a `BigInt`.
//@ 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.
for digit in self {
- a.do_action(digit);
+ a.do_action(digit); /*@*/
}
}
}
}
impl Action for PrintWithString {
- // Here we perform performs the actual printing of the prefix and the digit. We're not making use of our ability to
+ // Here we perform the actual printing of the prefix and the digit. We're not making use of our ability to
// change `self` here, but we could replace the prefix if we wanted.
fn do_action(&mut self, digit: u64) {
- println!("{}{}", self.prefix, digit);
+ println!("{}{}", self.prefix, digit); /*@*/
}
}
fn act<A: FnMut(u64)>(&self, mut a: A) {
for digit in self {
// We can call closures as if they were functions - but really, what's happening here is translated to essentially what we wrote above, in `act_v1`.
- a(digit);
+ a(digit); /*@*/
}
}
}
//@
//@ Since all these closures compile down to the pattern described above, there is actually no heap allocation going on here. This makes
//@ closures very efficient, and it makes optimization fairly trivial: The resulting code will look like you hand-rolled the loop in C.
- for i in v.iter().map(|n| n + offset).filter(|n| *n > threshold) {
+ for i in v.iter().map(|n| *n + offset).filter(|n| *n > threshold) {
println!("{}", i);
}
}
// And as a final example, one can also collect all elements of an iterator, and put them, e.g., in a vector.
fn filter_vec_by_divisor(v: &Vec<i32>, divisor: i32) -> Vec<i32> {
//@ Here, the return type of `collect` is inferred based on the return type of our function. In general, it can return anything implementing
- //@ [`FromIterator`](http://doc.rust-lang.org/stable/std/iter/trait.FromIterator.html). Notice that `iter` gives us an iterator over
+ //@ [`FromIterator`](https://doc.rust-lang.org/stable/std/iter/trait.FromIterator.html). Notice that `iter` gives us an iterator over
//@ borrowed `i32`, but we want to own them for the result, so we insert a `map` to dereference.
- v.iter().map(|n| *n).filter(|n| *n % divisor == 0).collect()
+ v.iter().map(|n| *n).filter(|n| *n % divisor == 0).collect() /*@*/
}
-// **Exercise 10.1**: Look up the [documentation of `Iterator`](http://doc.rust-lang.org/stable/std/iter/trait.Iterator.html) to learn about more functions
+// **Exercise 10.1**: Look up the [documentation of `Iterator`](https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html) to learn about more functions
// that can act on iterators. Try using some of them. What about a function that sums the even numbers of an iterator? Or a function that computes the
// product of those numbers that sit at odd positions? A function that checks whether a vector contains a certain number? Whether all numbers are
// smaller than some threshold? Be creative!
-//@ [index](main.html) | [previous](part08.html) | [next](main.html)
+//@ [index](main.html) | [previous](part09.html) | [raw source](https://www.ralfj.de/git/rust-101.git/blob_plain/HEAD:/workspace/src/part10.rs) | [next](part11.html)