std::ops::Drop - Rust (original) (raw)

Trait std::ops::Drop1.0.0 [−] [src]

#[lang = "drop"]

pub trait Drop { fn drop(&mut self); }

Used to run some code when a value goes out of scope. This is sometimes called a 'destructor'.

When a value goes out of scope, it will have its drop method called if its type implements Drop. Then, any fields the value contains will also be dropped recursively.

Because of this recursive dropping, you do not need to implement this trait unless your type needs its own destructor logic.

Refer to the chapter on Drop in The Rust Programming Languagefor some more elaboration.

The drop method is called when _x goes out of scope, and thereforemain prints Dropping!.

struct HasDrop;

impl Drop for HasDrop { fn drop(&mut self) { println!("Dropping!"); } }

fn main() { let _x = HasDrop; }Run

When outer goes out of scope, the drop method will be called first forOuter, then for Inner. Therefore, main prints Dropping Outer! and then Dropping Inner!.

struct Inner; struct Outer(Inner);

impl Drop for Inner { fn drop(&mut self) { println!("Dropping Inner!"); } }

impl Drop for Outer { fn drop(&mut self) { println!("Dropping Outer!"); } }

fn main() { let _x = Outer(Inner); }Run

_first is declared first and _second is declared second, so main will print Declared second! and then Declared first!.

struct PrintOnDrop(&'static str);

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

fn main() { let _first = PrintOnDrop("Declared first!"); let _second = PrintOnDrop("Declared second!"); }Run

fn [drop](#tymethod.drop)(&mut self)

Executes the destructor for this type.

This method is called implilcitly when the value goes out of scope, and cannot be called explicitly (this is compiler error E0040). However, the std::mem::drop function in the prelude can be used to call the argument's Drop implementation.

When this method has been called, self has not yet been deallocated. That only happens after the method is over. If this wasn't the case, self would be a dangling reference.

Given that a panic! will call drop as it unwinds, any panic!in a drop implementation will likely abort.

`impl<T, A> Drop for RawVec<T, A> where

A: Alloc, `[src]

fn [drop](#method.drop)(&mut self)[src]

Frees the memory owned by the RawVec without trying to Drop its contents.