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140 lines
2.2 KiB
Markdown
140 lines
2.2 KiB
Markdown
---
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id: a01bfc26-dece-4741-829b-d164ba9522bb
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title: Rust Iterators
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---
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# Syntax
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``` rust
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fn main() {
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let v1 = vec![1, 2, 3];
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let v1_iter = v1.iter();
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for val in v1_iter {
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println!("Got: {}", val);
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}
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}
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```
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# Iterator Trait
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All iterators implement a [trait](20200917163203-traits) named
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[Iterator](https://doc.rust-lang.org/std/iter/trait.Iterator.html)
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``` rust
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#![allow(unused)]
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fn main() {
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pub trait Iterator {
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type Item;
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fn next(&mut self) -> Option<Self::Item>;
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// methods with default implementations elided
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}
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}
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```
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# Iterator methods
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## next
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``` rust
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#[cfg(test)]
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mod tests {
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#[test]
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fn iterator_demonstration() {
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let v1 = vec![1, 2, 3];
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let mut v1_iter = v1.iter();
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assert_eq!(v1_iter.next(), Some(&1));
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assert_eq!(v1_iter.next(), Some(&2));
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assert_eq!(v1_iter.next(), Some(&3));
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assert_eq!(v1_iter.next(), None);
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}
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}
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fn main() {}
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```
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## sum
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``` rust
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#[cfg(test)]
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mod tests {
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#[test]
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fn iterator_sum() {
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let v1 = vec![1, 2, 3];
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let v1_iter = v1.iter();
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let total: i32 = v1_iter.sum();
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assert_eq!(total, 6);
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}
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}
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fn main() {}
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```
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# Methods that produce other Iterators
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By their nature iterators are lazy so the following won't work:
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``` rust
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fn main() {
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let v1: Vec<i32> = vec![1, 2, 3];
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v1.iter().map(|x| x + 1);
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}
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```
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The Iterator must be consumed, using the
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[collect](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.collect)
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method:
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``` rust
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fn main() {
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let v1: Vec<i32> = vec![1, 2, 3];
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let v2: Vec<_> = v1.iter().map(|x| x + 1).collect();
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assert_eq!(v2, vec![2, 3, 4]);
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}
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```
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# Creating your own Iterators
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``` rust
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struct Counter {
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count: u32,
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}
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impl Counter {
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fn new() -> Counter {
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Counter { count: 0 }
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}
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}
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impl Iterator for Counter {
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type Item = u32;
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fn next(&mut self) -> Option<Self::Item> {
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if self.count < 5 {
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self.count += 1;
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Some(self.count)
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} else {
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None
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}
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}
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}
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fn main() {
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let counter = Counter::new();
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for val in counter {
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println!("Got: {}", val);
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}
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}
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```
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