Ahh, I remember a while back reading a blog where the author talked about `std::mem::drop` being their favorite standard library function because they used this effect. It is literately defined as:

    pub fn drop<T>(_x: T) { }

https://doc.rust-lang.org/std/mem/fn.drop.html

Right, so drop is useless :) We can drop things fine without it. Since of course it's scope/ownership based and not something that's explicitly called.

Well,

  drop(x);

is a lot clearer than

  x;

So is drop like free, or is it something else?

Yes, it's effectively like free -- though C++'s "auto" is probably a closer idea.

The main difference to C's free is that you simply cannot double-free a value (without using unsafe). That's because a value is only dropped when it falls out of scope -- and since it values only have one owner (and references must not outlive values) there cannot be any dangling references after it's dropped.

The documentation for std::mem::drop is explaining that dropping a value is a property of the language and scoping rules -- thus there is nothing for the function to do other than take a value and let it go out of scope.

It’s more like delete in c++ because you can implement the Drop trait for a type in order to run code when it is dropped in order to clean up resources etc.

Drop is just what runs when a value goes out of scope. Like destructors in C++.