通过迭代器搜索
Iterator::find 是一个函数，它遍历迭代器并搜索满足某个条件的第一个值。如果没有值满足条件，则返回 None。其签名
pub trait Iterator {
// The type being iterated over.
type Item;
// `find` takes `&mut self` meaning the caller may be borrowed
// and modified, but not consumed.
fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where
// `FnMut` meaning any captured variable may at most be
// modified, not consumed. `&Self::Item` states it takes
// arguments to the closure by reference.
P: FnMut(&Self::Item) -> bool;
}fn main() { let vec1 = vec![1, 2, 3]; let vec2 = vec![4, 5, 6]; // `iter()` for vecs yields `&i32`. let mut iter = vec1.iter(); // `into_iter()` for vecs yields `i32`. let mut into_iter = vec2.into_iter(); // `iter()` for vecs yields `&i32`, and we want to reference one of its // items, so we have to destructure `&&i32` to `i32` println!("Find 2 in vec1: {:?}", iter .find(|&&x| x == 2)); // `into_iter()` for vecs yields `i32`, and we want to reference one of // its items, so we have to destructure `&i32` to `i32` println!("Find 2 in vec2: {:?}", into_iter.find(| &x| x == 2)); let array1 = [1, 2, 3]; let array2 = [4, 5, 6]; // `iter()` for arrays yields `&&i32` println!("Find 2 in array1: {:?}", array1.iter() .find(|&&x| x == 2)); // `into_iter()` for arrays yields `&i32` println!("Find 2 in array2: {:?}", array2.into_iter().find(|&x| x == 2)); }
Iterator::find 会给你一个指向该项的引用。但如果你想要该项的_索引_，请使用 Iterator::position。
fn main() { let vec = vec![1, 9, 3, 3, 13, 2]; // `iter()` for vecs yields `&i32` and `position()` does not take a reference, so // we have to destructure `&i32` to `i32` let index_of_first_even_number = vec.iter().position(|&x| x % 2 == 0); assert_eq!(index_of_first_even_number, Some(5)); // `into_iter()` for vecs yields `i32` and `position()` does not take a reference, so // we do not have to destructure let index_of_first_negative_number = vec.into_iter().position(|x| x < 0); assert_eq!(index_of_first_negative_number, None); }