vendor/thread_local/src/unreachable.rs

   1 // Copyright 2017 Amanieu d'Antras
   2 //
   3 // Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
   4 // http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
   5 // http://opensource.org/licenses/MIT>, at your option. This file may not be
   6 // copied, modified, or distributed except according to those terms.
   7
   8 //! # unreachable
   9 //! inlined from https://github.com/reem/rust-unreachable/
  10 //!
  11 //! An unreachable code optimization hint in stable rust, and some useful
  12 //! extension traits for `Option` and `Result`.
  13 //!
  14
  15 /// Hint to the optimizer that any code path which calls this function is
  16 /// statically unreachable and can be removed.
  17 ///
  18 /// Calling this function in reachable code invokes undefined behavior. Be
  19 /// very, very sure this is what you want; often, a simple `panic!` is more
  20 /// suitable.
  21 #[inline]
  22 pub unsafe fn unreachable() -> ! {
  23     /// The empty type for cases which can't occur.
  24     enum Void { }
  25     let x: &Void = ::std::mem::transmute(1usize);
  26     match *x {}
  27 }
  28
  29 /// An extension trait for `Option<T>` providing unchecked unwrapping methods.
  30 pub trait UncheckedOptionExt<T> {
  31     /// Get the value out of this Option without checking for None.
  32     unsafe fn unchecked_unwrap(self) -> T;
  33
  34     /// Assert that this Option is a None to the optimizer.
  35     unsafe fn unchecked_unwrap_none(self);
  36 }
  37
  38 /// An extension trait for `Result<T, E>` providing unchecked unwrapping methods.
  39 pub trait UncheckedResultExt<T, E> {
  40     /// Get the value out of this Result without checking for Err.
  41     unsafe fn unchecked_unwrap_ok(self) -> T;
  42
  43     /// Get the error out of this Result without checking for Ok.
  44     unsafe fn unchecked_unwrap_err(self) -> E;
  45 }
  46
  47 impl<T> UncheckedOptionExt<T> for Option<T> {
  48     unsafe fn unchecked_unwrap(self) -> T {
  49         match self {
  50             Some(x) => x,
  51             None => unreachable()
  52         }
  53     }
  54
  55     unsafe fn unchecked_unwrap_none(self) {
  56         if self.is_some() { unreachable() }
  57     }
  58 }
  59
  60 impl<T, E> UncheckedResultExt<T, E> for Result<T, E> {
  61     unsafe fn unchecked_unwrap_ok(self) -> T {
  62         match self {
  63             Ok(x) => x,
  64             Err(_) => unreachable()
  65         }
  66     }
  67
  68     unsafe fn unchecked_unwrap_err(self) -> E {
  69         match self {
  70             Ok(_) => unreachable(),
  71             Err(e) => e
  72         }
  73     }
  74 }