If you read the docs at your link it even says:
> This method is called implicitly when the value goes out of scope, and cannot be called explicitly (this is compiler error E0040).
> However, the mem::drop function in the prelude can be used to call the argument’s Drop implementation.
By the way the implementation of the function drop is just an empty function [2]; that's enough as local variables are destroyed on function return.
Mutable reference is a "borrow" which means you take a value from an owner and promise to return it back, and you cannot destroy a thing that you must return.
