+++ /dev/null
-// Rust-101, Part 10: Closures
-// ===========================
-
-use std::fmt;
-use part05::BigInt;
-
-
-// So, let us define a trait that demands that the type provides some method `do_action` on digits.
-trait Action {
- fn do_action(&mut self, digit: u64);
-}
-
-// Now we can write a function that takes some `a` of a type `A` such that we can call `do_action` on `a`, passing it every digit.
-impl BigInt {
- fn act_v1<A: Action>(&self, mut a: A) {
- for digit in self {
- unimplemented!()
- }
- }
-}
-
-struct PrintWithString {
- prefix: String,
-}
-
-impl Action for PrintWithString {
- // 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) {
- unimplemented!()
- }
-}
-
-// Finally, this function takes a `BigInt` and a prefix, and prints the digits with the given prefix.
-fn print_with_prefix_v1(b: &BigInt, prefix: String) {
- let my_action = PrintWithString { prefix: prefix };
- b.act_v1(my_action);
-}
-
-// Here's a small main function, demonstrating the code above in action. Remember to edit `main.rs` to run it.
-pub fn main() {
- let bignum = BigInt::new(1 << 63) + BigInt::new(1 << 16) + BigInt::new(1 << 63);
- print_with_prefix_v1(&bignum, "Digit: ".to_string());
-}
-
-// ## Closures
-
-// This defines `act` very similar to above, but now we demand `A` to be the type of a closure that mutates its borrowed environment,
-// takes a digit, and returns nothing.
-impl BigInt {
- 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`.
- unimplemented!()
- }
- }
-}
-
-// Now that we saw how to write a function that operates on closures, let's see how to write a closure.
-pub fn print_with_prefix(b: &BigInt, prefix: String) {
- b.act(|digit| println!("{}{}", prefix, digit) );
-}
-// You can change `main` to call this function, and you should notice - nothing, no difference in behavior.
-// But we wrote much less boilerplate code!
-
-// Remember that we decided to use the `FnMut` trait above? This means our closure could actually mutate its environment.
-// 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;
- b.act(|digit| { println!("{}: {}", count, digit); count = count +1; } );
- println!("There are {} digits", count);
-}
-
-// ## Fun with iterators and closures
-
-// Let's say we want to write a function that increments every entry of a `Vec` by some number, then looks for numbers larger than some threshold, and prints them.
-fn inc_print_even(v: &Vec<i32>, offset: i32, threshold: i32) {
- for i in v.iter().map(|n| *n + offset).filter(|n| *n > threshold) {
- println!("{}", i);
- }
-}
-
-// Sometimes it is useful to know both the position of some element in a list, and its value. That's where the `enumerate` function helps.
-fn print_enumerated<T: fmt::Display>(v: &Vec<T>) {
- for (i, t) in v.iter().enumerate() {
- println!("Position {}: {}", i, t);
- }
-}
-
-// 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> {
- unimplemented!()
-}
-
-// **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!
-
projects / rust-101.git / blobdiff