functions9.rs

pub trait Iterator {
    // The type being iterated over.
    type Item;

    // `any` takes `&mut self` meaning the caller may be borrowed
    // and modified, but not consumed.
    fn any<F>(&mut self, f: F) -> bool where
        // `FnMut` meaning any captured variable may at most be
        // modified, not consumed. `Self::Item` states it takes
        // arguments to the closure by value.
        F: FnMut(Self::Item) -> bool {}
}

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fn main() {
    let vec1 = vec![1, 2, 3];
    let vec2 = vec![4, 5, 6];

    // `iter()` for vecs yields `&i32`. Destructure to `i32`.
    println!("2 in vec1: {}", vec1.iter()     .any(|&x| x == 2));
    // `into_iter()` for vecs yields `i32`. No destructuring required.
    println!("2 in vec2: {}", vec2.into_iter().any(| x| x == 2));

    let array1 = [1, 2, 3];
    let array2 = [4, 5, 6];

    // `iter()` for arrays yields `&i32`.
    println!("2 in array1: {}", array1.iter()     .any(|&x| x == 2));
    // `into_iter()` for arrays unusually yields `&i32`.
    println!("2 in array2: {}", array2.into_iter().any(|&x| x == 2));
}