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Vector is a module in Rust that provides the container space to store values. It is a contiguous resizable array type, with heap-allocated contents. It is denoted by Vec<T>. Vectors in Rust have O(1) indexing and push and pop operations in vector also take O(1) complexity.
In Rust, there are several ways to initialize a vector. In order to initialize a vector via the new() method call, we use the double colon operator: let mut vec = Vec::new(); This call constructs a new, empty Vec<T> .
There is a swap method defined for &mut [T]. Since a Vec<T> can be mutably dereferenced as a &mut [T], this method can be called directly:
fn main() {
let mut numbers = vec![1, 2, 3];
println!("before = {:?}", numbers);
numbers.swap(0, 2);
println!("after = {:?}", numbers);
}
To implement this yourself, you have to write some unsafe code. Vec::swap is implemented like this:
fn swap(&mut self, a: usize, b: usize) {
unsafe {
// Can't take two mutable loans from one vector, so instead just cast
// them to their raw pointers to do the swap
let pa: *mut T = &mut self[a];
let pb: *mut T = &mut self[b];
ptr::swap(pa, pb);
}
}
It takes two raw pointers from the vector and uses ptr::swap to swap them safely.
There is also a mem::swap(&mut T, &mut T) when you need to swap two distinct variables. That cannot be used here because Rust won't allow taking two mutable borrows from the same vector.
As mentioned by @gsingh2011, the accepted answer is no longer good approach. With current Rust this code works fine:
fn main() {
let mut numbers = vec![1, 2, 3];
println!("before = {:?}", numbers);
numbers.swap(0, 2);
println!("after = {:?}", numbers);
}
try it here
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