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//! This crate gives a generic way to add a callback to any dropping value
//!
//! You may use this for debugging values, see the [struct documentation](struct.DropGuard.html) or the [standalone examples](https://github.com/dns2utf8/drop_guard/tree/master/examples).
//!
//! # Example:
//!
//! ```
//! extern crate drop_guard;
//!
//! use drop_guard::guard;
//!
//! use std::thread::{spawn, sleep};
//! use std::time::Duration;
//!
//! fn main() {
//! let _ = guard(spawn(move || {
//! sleep(Duration::from_secs(2));
//! println!("println! from thread");
//! })
//! , |join_handle| join_handle.join().unwrap());
//!
//! println!("Waiting for thread ...");
//! }
//! ```
//!
use std::boxed::Box;
use std::ops::{Deref, DerefMut, Drop, FnMut};
#[must_use]
#[inline]
pub fn guard<T: Sized, F: FnMut(T)>(thing: T, func: F) -> DropGuard<T, F> {
DropGuard {
data: Some(thing),
func: Box::new(func),
}
}
/// The DropGuard will remain to `Send` and `Sync` from `T`.
///
/// # Examples
///
/// The `LinkedList<T>` is `Send`.
/// So the `DropGuard` will be too, but it will not be `Sync`:
///
/// ```
/// use drop_guard::guard;
/// use std::collections::LinkedList;
/// use std::thread;
///
/// let list: LinkedList<u32> = LinkedList::new();
///
/// let a_list = guard(list, |_| {});
///
/// // Send the guarded list to another thread
/// thread::spawn(move || {
/// assert_eq!(0, a_list.len());
/// }).join();
/// ```
pub struct DropGuard<T, F: FnMut(T)> {
data: Option<T>,
func: Box<F>,
}
impl<T: Sized, F: FnMut(T)> DropGuard<T, F> {
/// Creates a new guard taking in your data and a function.
///
/// ```
/// use drop_guard::guard;
///
/// let s = String::from("a commonString");
/// let mut s = guard(s, |final_string| println!("s became {} at last", final_string));
///
/// // much code and time passes by ...
/// *s = "a rainbow".to_string();
///
/// // by the end of this function the String will have become a rainbow
/// ```
#[must_use]
#[inline]
#[deprecated(note = "use `drop_guard::guard` that is shorter")]
pub fn new(data: T, func: F) -> DropGuard<T, F> {
guard(data, func)
}
}
/// Use the captured value.
///
/// ```
/// use drop_guard::guard;
///
/// let val = guard(42usize, |_| {});
/// assert_eq!(42, *val);
/// ```
impl<T, F: FnMut(T)> Deref for DropGuard<T, F> {
type Target = T;
fn deref(&self) -> &T {
&self.data.as_ref().expect("the data is here until the drop")
}
}
/// Modify the captured value.
///
/// ```
/// use drop_guard::guard;
///
/// let mut val = guard(vec![2, 3, 4], |_| {});
/// assert_eq!(3, val.len());
///
/// val.push(5);
/// assert_eq!(4, val.len());
/// ```
impl<T, F: FnMut(T)> DerefMut for DropGuard<T, F> {
fn deref_mut(&mut self) -> &mut T {
self.data.as_mut().expect("the data is here until the drop")
}
}
/// React to dropping the value.
/// In this example we measure the time the value is alive.
///
/// ```
/// use drop_guard::guard;
/// use std::time::Instant;
///
/// let start_time = Instant::now();
/// let val = guard(42usize, |_| {
/// let time_alive = start_time.elapsed();
/// println!("value lived for {}ns", time_alive.subsec_nanos())
/// });
/// assert_eq!(42, *val);
/// ```
impl<T, F: FnMut(T)> Drop for DropGuard<T, F> {
fn drop(&mut self) {
let mut data: Option<T> = None;
std::mem::swap(&mut data, &mut self.data);
let ref mut f = self.func;
f(data.expect("the data is here until the drop"));
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;
#[test]
fn it_works() {
let mut i = 0;
{
let _ = guard(0, |_| i = 42);
}
assert_eq!(42, i);
}
#[test]
fn deref() {
let g = guard(5usize, |_| {});
assert_eq!(5usize, *g);
}
#[test]
fn deref_mut() {
let mut g = guard(5usize, |_| {});
*g = 12;
assert_eq!(12usize, *g);
}
#[test]
fn drop_change() {
let a = Arc::new(AtomicUsize::new(9));
{
let _ = guard(a.clone(), |i| i.store(42, Ordering::Relaxed));
}
assert_eq!(42usize, a.load(Ordering::Relaxed));
}
#[test]
fn keep_sync_shared_data() {
fn assert_sync<T: Sync>(_: T) {}
let g = guard(vec![0], |_| {});
assert_sync(g);
}
#[test]
fn keep_send_shared_data() {
fn assert_send<T: Send>(_: T) {}
let g = guard(vec![0], |_| {});
assert_send(g);
}
}