Rust by Example

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 unusually yields `&i32`

println!("Find 2 in array2: {:?}", array2.into_iter().find(|&&x| x == 2));

}

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Iterator::find gives you a reference to the item. But if you want the index of the item, use Iterator::position.

fn main() {

let vec = vec![1, 9, 3, 3, 13, 2];

let index_of_first_even_number = vec.iter().position(|x| x % 2 == 0);

assert_eq!(index_of_first_even_number, Some(5));

let index_of_first_negative_number = vec.iter().position(|x| x < &0);

assert_eq!(index_of_first_negative_number, None);

}

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See also:

std::iter::Iterator::find

std::iter::Iterator::find_map

std::iter::Iterator::position

std::iter::Iterator::rposition

Higher Order Functions

Rust provides Higher Order Functions (HOF). These are functions that take one or more functions and/or produce a more useful function. HOFs and lazy iterators give Rust its functional flavor.

fn is_odd(n: u32) -> bool {

n % 2 == 1

}

fn main() {