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|
//! # drop_bomb
//!
//! `drop_bomb` provides two types, `DropBomb` and `DebugDropBomb`,
//! which panic in `drop` with a specified message unless
//! defused. This is useful as a building-block for runtime-checked
//! linear types.
//!
//! For example, one can build a variant of `BufWriter` which enforces
//! handling of errors during flush.
//!
//! ```rust
//! extern crate drop_bomb;
//!
//! use std::io::{Write, BufWriter, Result};
//! use drop_bomb::DropBomb;
//!
//! struct CheckedBufWriter<W: Write> {
//! inner: BufWriter<W>,
//! bomb: DropBomb,
//! }
//!
//! impl<W: Write> CheckedBufWriter<W> {
//! fn new(inner: BufWriter<W>) -> CheckedBufWriter<W> {
//! let bomb = DropBomb::new(
//! "CheckedBufWriter must be explicitly closed \
//! to handle potential errors on flush"
//! );
//! CheckedBufWriter { inner, bomb }
//! }
//!
//! fn close(mut self) -> Result<()> {
//! self.bomb.defuse();
//! self.inner.flush()?;
//! Ok(())
//! }
//! }
//! ```
//!
//! ## Notes:
//!
//! * Bombs do nothing if a thread is already panicking.
//! * When `#[cfg(debug_assertions)]` is disabled, `DebugDropBomb` is
//! always defused and has a zero size.
use std::borrow::Cow;
#[derive(Debug)]
#[must_use]
pub struct DropBomb(RealBomb);
impl DropBomb {
pub fn new(msg: impl Into<Cow<'static, str>>) -> DropBomb {
DropBomb(RealBomb::new(msg.into()))
}
pub fn defuse(&mut self) {
self.set_defused(true)
}
pub fn set_defused(&mut self, defused: bool) {
self.0.set_defused(defused)
}
pub fn is_defused(&self) -> bool {
self.0.is_defused()
}
}
#[derive(Debug)]
#[must_use]
pub struct DebugDropBomb(DebugBomb);
impl DebugDropBomb {
pub fn new(msg: impl Into<Cow<'static, str>>) -> DebugDropBomb {
DebugDropBomb(DebugBomb::new(msg.into()))
}
pub fn defuse(&mut self) {
self.set_defused(true)
}
pub fn set_defused(&mut self, defused: bool) {
self.0.set_defused(defused)
}
pub fn is_defused(&self) -> bool {
self.0.is_defused()
}
}
#[cfg(debug_assertions)]
type DebugBomb = RealBomb;
#[cfg(not(debug_assertions))]
type DebugBomb = FakeBomb;
#[derive(Debug)]
struct RealBomb {
msg: Cow<'static, str>,
defused: bool,
}
impl RealBomb {
fn new(msg: Cow<'static, str>) -> RealBomb {
RealBomb {
msg: msg.into(),
defused: false,
}
}
fn set_defused(&mut self, defused: bool) {
self.defused = defused
}
fn is_defused(&self) -> bool {
self.defused
}
}
impl Drop for RealBomb {
fn drop(&mut self) {
if !self.defused && !::std::thread::panicking() {
panic!("{}", self.msg)
}
}
}
#[derive(Debug)]
#[cfg(not(debug_assertions))]
struct FakeBomb {}
#[cfg(not(debug_assertions))]
impl FakeBomb {
fn new(_msg: Cow<'static, str>) -> FakeBomb {
FakeBomb {}
}
fn set_defused(&mut self, _defused: bool) {}
fn is_defused(&self) -> bool {
true
}
}
#[cfg(not(debug_assertions))]
impl Drop for FakeBomb {
fn drop(&mut self) {}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
#[should_panic(expected = "Kaboom")]
fn armed_bomb_bombs() {
let _b = DropBomb::new("Kaboom");
}
#[test]
fn defused_bomb_is_safe() {
let mut b = DropBomb::new("Kaboom");
assert!(!b.is_defused());
b.defuse();
assert!(b.is_defused());
}
#[test]
#[should_panic(expected = r#"printf("sucks to be you"); exit(666);"#)]
fn no_double_panics() {
let _b = DropBomb::new("Kaboom");
panic!(r#"printf("sucks to be you"); exit(666);"#)
}
#[test]
#[should_panic(expected = "Kaboom")]
#[cfg(debug_assertions)]
fn debug_bomb_bombs_if_debug() {
let _b = DebugDropBomb::new("Kaboom");
}
#[test]
#[cfg(not(debug_assertions))]
fn debug_bomb_bombs_if_debug() {
let _b = DebugDropBomb::new("Kaboom");
}
#[test]
fn defused_bomb_is_safe_if_debug() {
let mut b = DebugDropBomb::new("Kaboom");
#[cfg(debug_assertions)]
assert!(!b.is_defused());
#[cfg(not(debug_assertions))]
assert!(b.is_defused());
b.defuse();
assert!(b.is_defused());
}
#[test]
#[should_panic(expected = r#"printf("sucks to be you"); exit(666);"#)]
fn no_double_panics_if_debug() {
let _b = DebugDropBomb::new("Kaboom");
panic!(r#"printf("sucks to be you"); exit(666);"#)
}
#[test]
#[cfg(not(debug_assertions))]
fn debug_bomb_is_zst() {
assert_eq!(::std::mem::size_of::<DebugDropBomb>(), 0);
}
#[test]
fn check_traits() {
fn assert_traits<T: ::std::fmt::Debug + Send + Sync>() {}
assert_traits::<DropBomb>();
assert_traits::<DebugDropBomb>();
}
}
|
