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80 lines
2.3 KiB
Rust
80 lines
2.3 KiB
Rust
// ./src/trait/iter.md
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struct Fibonacci {
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curr: u32,
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next: u32,
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}
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// Implement `Iterator` for `Fibonacci`.
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// The `Iterator` trait only requires a method to be defined for the `next` element.
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impl Iterator for Fibonacci {
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// We can refer to this type using Self::Item
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type Item = u32;
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// Here, we define the sequence using `.curr` and `.next`.
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// The return type is `Option<T>`:
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// * When the `Iterator` is finished, `None` is returned.
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// * Otherwise, the next value is wrapped in `Some` and returned.
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// We use Self::Item in the return type, so we can change
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// the type without having to update the function signatures.
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fn next(&mut self) -> Option<Self::Item> {
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let current = self.curr;
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self.curr = self.next;
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self.next = current + self.next;
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// Since there's no endpoint to a Fibonacci sequence, the `Iterator`
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// will never return `None`, and `Some` is always returned.
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Some(current)
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}
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}
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// Returns a Fibonacci sequence generator
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fn fibonacci() -> Fibonacci {
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Fibonacci { curr: 0, next: 1 }
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}
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fn part0() {
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// `0..3` is an `Iterator` that generates: 0, 1, and 2.
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let mut sequence = 0..3;
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println!("Four consecutive `next` calls on 0..3");
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println!("> {:?}", sequence.next());
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println!("> {:?}", sequence.next());
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println!("> {:?}", sequence.next());
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println!("> {:?}", sequence.next());
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// `for` works through an `Iterator` until it returns `None`.
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// Each `Some` value is unwrapped and bound to a variable (here, `i`).
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println!("Iterate through 0..3 using `for`");
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for i in 0..3 {
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println!("> {}", i);
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}
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// The `take(n)` method reduces an `Iterator` to its first `n` terms.
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println!("The first four terms of the Fibonacci sequence are: ");
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for i in fibonacci().take(4) {
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println!("> {}", i);
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}
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// The `skip(n)` method shortens an `Iterator` by dropping its first `n` terms.
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println!("The next four terms of the Fibonacci sequence are: ");
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for i in fibonacci().skip(4).take(4) {
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println!("> {}", i);
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}
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let array = [1u32, 3, 3, 7];
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// The `iter` method produces an `Iterator` over an array/slice.
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println!("Iterate the following array {:?}", &array);
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for i in array.iter() {
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println!("> {}", i);
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}
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}
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pub fn main() {
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part0();
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}
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