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use std::mem;
/**
* Leak a piece of data by never calling its destructor
*
* Useful for things that are going to be used for the life of the program, but aren't technically
* static (because they are created in response to arguments, environment, or other
* configuration/data read at program start).
*
*
*
* Notable changes:
* - for user convenience, leak() is a non-static method
* - Return `&T` instead of `&mut T`
*
* While it would be ideal to return a `&'a mut T`, we apparently can't do that due to limitations
* in rust's borrow checker causing soundness issues. Details are in the RFC liked above.
*/
pub trait Leak<T : ?Sized> {
fn leak<'a>(self) -> &'a T where T: 'a;
}
impl<T : ?Sized> Leak<T> for Box<T> {
fn leak<'a>(self) -> &'a T where T: 'a {
let r = Self::into_raw(self);
unsafe { &mut *r }
}
}
/*
* while String and Vec<T> could have impls in terms of Box, we specialize them because their
* conversions to Box (into_boxed_slice and into_boxed_str) result in resizing underlying storage
*/
impl Leak<str> for String {
fn leak<'a>(mut self) -> &'a str where Self: 'a {
let r: *mut str = &mut self[..];
mem::forget(self);
unsafe { &mut *r }
}
}
impl<T> Leak<[T]> for Vec<T> {
fn leak<'a>(mut self) -> &'a [T] where [T]: 'a {
let r: *mut [T] = &mut self[..];
mem::forget(self);
unsafe { &mut *r }
}
}
#[cfg(test)]
mod test {
#[test]
fn leak_str() {
use super::Leak;
use std::borrow::ToOwned;
let v = "hi";
let leaked : &str = {
let o = v.to_owned();
o.leak()
};
assert_eq!(leaked, v);
let leaked : &'static str = {
let o = v.to_owned();
o.leak()
};
assert_eq!(leaked, v);
}
#[test]
fn leak_empty_str() {
use super::Leak;
use std::borrow::ToOwned;
let v = "";
let leaked : &'static str = {
let o = v.to_owned();
o.leak()
};
assert_eq!(leaked, v);
}
#[test]
fn leak_vec() {
use super::Leak;
let v = vec![3, 5];
let leaked : &'static [u8] = {
let o = v.clone();
o.leak()
};
assert_eq!(leaked, &*v);
}
#[test]
fn leak_empty_vec() {
use super::Leak;
let v = vec![];
let leaked : &'static [u8] = {
let o = v.clone();
o.leak()
};
assert_eq!(leaked, &*v);
}
#[test]
fn leak_box() {
use super::Leak;
let v : Box<[&str]> = vec!["hi", "there"].into_boxed_slice();
let leaked : &'static [&str] = {
let o = v.clone();
o.leak()
};
assert_eq!(leaked, &*v);
}
#[test]
fn leak_nested() {
use super::Leak;
let v : Box<Vec<&str>> = Box::new(vec!["hi", "there"]);
let leaked : &'static [&str] = {
let o = v.clone();
o.leak()
};
assert_eq!(leaked, &**v);
}
}