The ref pattern

When doing pattern matching or destructuring via the let binding, the ref keyword can be used to take references to the fields of a struct/tuple. The example below shows a few instances where this can be useful:

#[derive(Clone, Copy)]

struct Point { x: i32, y: i32 }

fn main() {

let c = 'Q';

// A `ref` borrow on the left side of an assignment is equivalent to

// an `&` borrow on the right side.

let ref ref_c1 = c;

let ref_c2 = &c;

println!("ref_c1 equals ref_c2: {}", *ref_c1 == *ref_c2);

let point = Point { x: 0, y: 0 };

// `ref` is also valid when destructuring a struct.

let _copy_of_x = {

// `ref_to_x` is a reference to the `x` field of `point`.

let Point { x: ref ref_to_x, y: _ } = point;

// Return a copy of the `x` field of `point`.

*ref_to_x

};

// A mutable copy of `point`

let mut mutable_point = point;

{

// `ref` can be paired with `mut` to take mutable references.

let Point { x: _, y: ref mut mut_ref_to_y } = mutable_point;

// Mutate the `y` field of `mutable_point` via a mutable reference.

*mut_ref_to_y = 1;

}

println!("point is ({}, {})", point.x, point.y);

println!("mutable_point is ({}, {})", mutable_point.x, mutable_point.y);

// A mutable tuple that includes a pointer

let mut mutable_tuple = (Box::new(5u32), 3u32);

{

// Destructure `mutable_tuple` to change the value of `last`.

let (_, ref mut last) = mutable_tuple;

*last = 2u32;

}

println!("tuple is {:?}", mutable_tuple);

}

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