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// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*!
The Finally trait provides a method, `finally` on
stack closures that emulates Java-style try/finally blocks.
Using the `finally` method is sometimes convenient, but the type rules
prohibit any shared, mutable state between the "try" case and the
"finally" case. For advanced cases, the `try_finally` function can
also be used. See that function for more details.
# Example
```
use std::finally::Finally;
(|| {
// ...
}).finally(|| {
// this code is always run
})
```
*/
#![experimental]
use ops::Drop;
/// A trait for executing a destructor unconditionally after a block of code,
/// regardless of whether the blocked fails.
pub trait Finally<T> {
/// Executes this object, unconditionally running `dtor` after this block of
/// code has run.
fn finally(&mut self, dtor: ||) -> T;
}
impl<'a,T> Finally<T> for ||: 'a -> T {
fn finally(&mut self, dtor: ||) -> T {
try_finally(&mut (), self,
|_, f| (*f)(),
|_| dtor())
}
}
impl<T> Finally<T> for fn() -> T {
fn finally(&mut self, dtor: ||) -> T {
try_finally(&mut (), (),
|_, _| (*self)(),
|_| dtor())
}
}
/**
* The most general form of the `finally` functions. The function
* `try_fn` will be invoked first; whether or not it fails, the
* function `finally_fn` will be invoked next. The two parameters
* `mutate` and `drop` are used to thread state through the two
* closures. `mutate` is used for any shared, mutable state that both
* closures require access to; `drop` is used for any state that the
* `try_fn` requires ownership of.
*
* **WARNING:** While shared, mutable state between the try and finally
* function is often necessary, one must be very careful; the `try`
* function could have failed at any point, so the values of the shared
* state may be inconsistent.
*
* # Example
*
* ```
* use std::finally::try_finally;
*
* struct State<'a> { buffer: &'a mut [u8], len: uint }
* # let mut buf = [];
* let mut state = State { buffer: buf, len: 0 };
* try_finally(
* &mut state, (),
* |state, ()| {
* // use state.buffer, state.len
* },
* |state| {
* // use state.buffer, state.len to cleanup
* })
* ```
*/
pub fn try_finally<T,U,R>(mutate: &mut T,
drop: U,
try_fn: |&mut T, U| -> R,
finally_fn: |&mut T|)
-> R {
let f = Finallyalizer {
mutate: mutate,
dtor: finally_fn,
};
try_fn(&mut *f.mutate, drop)
}
struct Finallyalizer<'a,A> {
mutate: &'a mut A,
dtor: |&mut A|: 'a
}
#[unsafe_destructor]
impl<'a,A> Drop for Finallyalizer<'a,A> {
#[inline]
fn drop(&mut self) {
(self.dtor)(self.mutate);
}
}
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