rayon-hash 0.5.0

// Copyright 2012-2014 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.

use std::fmt;
use std::marker::PhantomData;
use std::ptr::NonNull;

/// A wrapper around a raw non-null `*mut T` that indicates that the possessor
/// of this wrapper owns the referent. Useful for building abstractions like
/// `Box<T>`, `Vec<T>`, `String`, and `HashMap<K, V>`.
///
/// Unlike `*mut T`, `Unique<T>` behaves "as if" it were an instance of `T`.
/// It implements `Send`/`Sync` if `T` is `Send`/`Sync`. It also implies
/// the kind of strong aliasing guarantees an instance of `T` can expect:
/// the referent of the pointer should not be modified without a unique path to
/// its owning Unique.
///
/// If you're uncertain of whether it's correct to use `Unique` for your purposes,
/// consider using `NonNull`, which has weaker semantics.
///
/// Unlike `*mut T`, the pointer must always be non-null, even if the pointer
/// is never dereferenced. This is so that enums may use this forbidden value
/// as a discriminant -- `Option<Unique<T>>` has the same size as `Unique<T>`.
/// However the pointer may still dangle if it isn't dereferenced.
///
/// Unlike `*mut T`, `Unique<T>` is covariant over `T`. This should always be correct
/// for any type which upholds Unique's aliasing requirements.
// #[unstable(feature = "ptr_internals", issue = "0",
//            reason = "use NonNull instead and consider PhantomData<T> \
//                      (if you also use #[may_dangle]), Send, and/or Sync")]
// #[doc(hidden)]
#[repr(transparent)]
pub(crate) struct Unique<T: ?Sized> {
    pointer: NonNull<T>,
    // NOTE: this marker has no consequences for variance, but is necessary
    // for dropck to understand that we logically own a `T`.
    //
    // For details, see:
    // https://github.com/rust-lang/rfcs/blob/master/text/0769-sound-generic-drop.md#phantom-data
    _marker: PhantomData<T>,
}

// #[unstable(feature = "ptr_internals", issue = "0")]
impl<T: ?Sized> fmt::Debug for Unique<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Pointer::fmt(&self.as_ptr(), f)
    }
}

/// `Unique` pointers are `Send` if `T` is `Send` because the data they
/// reference is unaliased. Note that this aliasing invariant is
/// unenforced by the type system; the abstraction using the
/// `Unique` must enforce it.
// #[unstable(feature = "ptr_internals", issue = "0")]
unsafe impl<T: Send + ?Sized> Send for Unique<T> { }

/// `Unique` pointers are `Sync` if `T` is `Sync` because the data they
/// reference is unaliased. Note that this aliasing invariant is
/// unenforced by the type system; the abstraction using the
/// `Unique` must enforce it.
// #[unstable(feature = "ptr_internals", issue = "0")]
unsafe impl<T: Sync + ?Sized> Sync for Unique<T> { }

// #[unstable(feature = "ptr_internals", issue = "0")]
impl<T: ?Sized> Unique<T> {
    /// Creates a new `Unique`.
    ///
    /// # Safety
    ///
    /// `ptr` must be non-null.
    pub(crate) unsafe fn new_unchecked(ptr: *mut T) -> Self {
        Unique { pointer: NonNull::new_unchecked(ptr), _marker: PhantomData }
    }

    /// Acquires the underlying `*mut` pointer.
    pub(crate) fn as_ptr(self) -> *mut T {
        self.pointer.as_ptr()
    }
}

// #[unstable(feature = "ptr_internals", issue = "0")]
impl<T: ?Sized> Clone for Unique<T> {
    fn clone(&self) -> Self {
        *self
    }
}

// #[unstable(feature = "ptr_internals", issue = "0")]
impl<T: ?Sized> Copy for Unique<T> { }