Is the resource of a shadowed variable binding freed immediately?

by

No, it is not freed immediately. Let’s make the code tell us itself:

struct Foo(u8);

impl Drop for Foo {
    fn drop(&mut self) {
        println!("Dropping {}", self.0)
    }
}

fn main() {
    let a = Foo(1);
    let b = Foo(2);

    println!("All done!");
}

The output is:

All done!
Dropping 2
Dropping 1

For me, this has come in handy in cases where you transform the variable into some sort of reference, but don’t care about the original. For example:

fn main() {
    let msg = String::from("   hello world   \n");
    let msg = msg.trim();
}

More Related Contents:

  1. Why do I need to import a trait to use the methods it defines for a type?
  2. Why is adding a lifetime to a trait with the plus operator (Iterator + ‘a) needed?
  3. Should trait bounds be duplicated in struct and impl?
  4. Can I do type introspection with trait objects and then downcast it?
  5. Cannot borrow as mutable more than once at a time in one code – but can in another very similar
  6. How can I perform parallel asynchronous HTTP GET requests with reqwest?
  7. Is it considered a bad practice to implement Deref for newtypes?
  8. Implementing a trait for multiple types at once
  9. Convert a String to int?
  10. How do I get an owned value out of a `Box`?
  11. How do I borrow a RefCell, find a key, and return a reference to the result? [duplicate]
  12. Converting from Option to Option
  13. Is there a way other than traits to add methods to a type I don’t own?
  14. What is the difference between `e1` and `&e2` when used as the for-loop variable?
  15. Why doesn’t println! work in Rust unit tests?
  16. How do you use parent module imports in Rust?
  17. What does ‘let x = x’ do in Rust?
  18. Is it possible to return either a borrowed or owned type in Rust?
  19. How can I call a raw address from Rust?
  20. Is there a way to perform an index access to an instance of a struct?
  21. How to take ownership of T from Arc?
  22. How to use a local unpublished crate?
  23. Why do I get “type annotations needed” when using Iterator::collect?
  24. Why can I iterate over a slice twice, but not a vector?
  25. How to idiomatically alias a crate in Rust 2018?
  26. Cannot borrow immutable borrowed content as mutable
  27. Why do I get “does not live long enough” in a return value?
  28. Why does the compiler not complain that an iterator moved to a for loop is immutable?
  29. Why doesn’t the lifetime of a mutable borrow end when the function call is complete?
  30. Lazy sequence generation in Rust

Leave a Comment