RAII all too rusty - 0

I know most of us know what RAII is but we still gotta talk it for those who aren't aware.

So, What exactly is it?

It's very simple if you are coming from something like C++:

• acquire a resource x
• automatically clean it up when x goes out of scope.

So no manual free() or close().

Note: I am talking about a resource in general, i.e. not limited to basic Vectors, HashMaps and such.

Rust (🦀):

{
    let arr = vec![1,2,3,4]; //automatically allocated on heap
}
// as soon as x goes out of scope its cleaned up.

Again this is not just limited to datatypes:

{
    use std::fs::File;

    let file = File::open("foo.txt");
    // do stuff to the file
}
// as soon as file goes out of scope its cleaned up.

Rust achieves this by something called the Drop trait. Every resource which implements RAII, implements the Drop trait. And whenever the resource goes out scope aka the ownership ends, drop() gets called.

You can also implement Drop for your own resources.

struct EatLunch;

impl Drop for EatLunch {
    fn drop(&mut self) {
        println!("Washing hands");
    }
}

fn main() {
    let me = EatLunch; // I eat lunch
}
// As soon as I am done eating, I wash my hands
//because drop() is called.