      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297

    use crate::cmp::Ordering;
    use crate::convert::From;
    use crate::fmt;
    use crate::hash;
    use crate::marker::Unsize;
    use crate::mem;
    use crate::ops::{CoerceUnsized, DispatchFromDyn};
    use crate::ptr::Unique;

    /// `*mut T` but non-zero and covariant.
    ///
    /// This is often the correct thing to use when building data structures using
    /// raw pointers, but is ultimately more dangerous to use because of its additional
    /// properties. If you're not sure if you should use `NonNull<T>`, just use `*mut T`!
    ///
    /// 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<NonNull<T>>` has the same size as `*mut T`.
    /// However the pointer may still dangle if it isn't dereferenced.
    ///
    /// Unlike `*mut T`, `NonNull<T>` is covariant over `T`. If this is incorrect
    /// for your use case, you should include some [`PhantomData`] in your type to
    /// provide invariance, such as `PhantomData<Cell<T>>` or `PhantomData<&'a mut T>`.
    /// Usually this won't be necessary; covariance is correct for most safe abstractions,
    /// such as `Box`, `Rc`, `Arc`, `Vec`, and `LinkedList`. This is the case because they
    /// provide a public API that follows the normal shared XOR mutable rules of Rust.
    ///
    /// Notice that `NonNull<T>` has a `From` instance for `&T`. However, this does
    /// not change the fact that mutating through a (pointer derived from a) shared
    /// reference is undefined behavior unless the mutation happens inside an
    /// [`UnsafeCell<T>`]. The same goes for creating a mutable reference from a shared
    /// reference. When using this `From` instance without an `UnsafeCell<T>`,
    /// it is your responsibility to ensure that `as_mut` is never called, and `as_ptr`
    /// is never used for mutation.
    ///
    /// [`PhantomData`]: ../marker/struct.PhantomData.html
    /// [`UnsafeCell<T>`]: ../cell/struct.UnsafeCell.html
    #[stable(feature = "nonnull", since = "1.25.0")]
    #[repr(transparent)]
    #[rustc_layout_scalar_valid_range_start(1)]
    #[rustc_nonnull_optimization_guaranteed]
    pub struct NonNull<T: ?Sized> {
        pointer: *const T,
    }

    /// `NonNull` pointers are not `Send` because the data they reference may be aliased.
    // N.B., this impl is unnecessary, but should provide better error messages.
    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> !Send for NonNull<T> {}

    /// `NonNull` pointers are not `Sync` because the data they reference may be aliased.
    // N.B., this impl is unnecessary, but should provide better error messages.
    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> !Sync for NonNull<T> {}

    impl<T: Sized> NonNull<T> {
        /// Creates a new `NonNull` that is dangling, but well-aligned.
        ///
        /// This is useful for initializing types which lazily allocate, like
        /// `Vec::new` does.
        ///
        /// Note that the pointer value may potentially represent a valid pointer to
        /// a `T`, which means this must not be used as a "not yet initialized"
        /// sentinel value. Types that lazily allocate must track initialization by
        /// some other means.
        #[stable(feature = "nonnull", since = "1.25.0")]
        #[rustc_const_stable(feature = "const_nonnull_dangling", since = "1.32.0")]
        #[inline]
        pub const fn dangling() -> Self {
            // SAFETY: mem::align_of() returns a non-zero usize which is then casted
            // to a *mut T. Therefore, `ptr` is not null and the conditions for
            // calling new_unchecked() are respected.
            unsafe {
                let ptr = mem::align_of::<T>() as *mut T;
                NonNull::new_unchecked(ptr)
            }
        }
    }

    impl<T: ?Sized> NonNull<T> {
        /// Creates a new `NonNull`.
        ///
        /// # Safety
        ///
        /// `ptr` must be non-null.
        #[stable(feature = "nonnull", since = "1.25.0")]
        #[rustc_const_stable(feature = "const_nonnull_new_unchecked", since = "1.32.0")]
        #[inline]
        pub const unsafe fn new_unchecked(ptr: *mut T) -> Self {
            NonNull { pointer: ptr as _ }
        }

        /// Creates a new `NonNull` if `ptr` is non-null.
        #[stable(feature = "nonnull", since = "1.25.0")]
        #[inline]
        pub fn new(ptr: *mut T) -> Option<Self> {
            if !ptr.is_null() {
                // SAFETY: The pointer is already checked and is not null
                Some(unsafe { Self::new_unchecked(ptr) })
            } else {
                None
            }
        }

        /// Acquires the underlying `*mut` pointer.
        #[stable(feature = "nonnull", since = "1.25.0")]
        #[rustc_const_stable(feature = "const_nonnull_as_ptr", since = "1.32.0")]
        #[inline]
        pub const fn as_ptr(self) -> *mut T {
            self.pointer as *mut T
        }

        /// Dereferences the content.
        ///
        /// The resulting lifetime is bound to self so this behaves "as if"
        /// it were actually an instance of T that is getting borrowed. If a longer
        /// (unbound) lifetime is needed, use `&*my_ptr.as_ptr()`.
        #[stable(feature = "nonnull", since = "1.25.0")]
        #[inline]
        pub unsafe fn as_ref(&self) -> &T {
            &*self.as_ptr()
        }

        /// Mutably dereferences the content.
        ///
        /// The resulting lifetime is bound to self so this behaves "as if"
        /// it were actually an instance of T that is getting borrowed. If a longer
        /// (unbound) lifetime is needed, use `&mut *my_ptr.as_ptr()`.
        #[stable(feature = "nonnull", since = "1.25.0")]
        #[inline]
        pub unsafe fn as_mut(&mut self) -> &mut T {
            &mut *self.as_ptr()
        }

        /// Casts to a pointer of another type.
        #[stable(feature = "nonnull_cast", since = "1.27.0")]
        #[rustc_const_stable(feature = "const_nonnull_cast", since = "1.32.0")]
        #[inline]
        pub const fn cast<U>(self) -> NonNull<U> {
            // SAFETY: `self` is a `NonNull` pointer which is necessarily non-null
            unsafe { NonNull::new_unchecked(self.as_ptr() as *mut U) }
        }
    }

    impl<T> NonNull<[T]> {
        /// Creates a non-null raw slice from a thin pointer and a length.
        ///
        /// The `len` argument is the number of **elements**, not the number of bytes.
        ///
        /// This function is safe, but dereferencing the return value is unsafe.
        /// See the documentation of [`slice::from_raw_parts`] for slice safety requirements.
        ///
        /// [`slice::from_raw_parts`]: ../../std/slice/fn.from_raw_parts.html
        ///
        /// # Examples
        ///
        /// ```rust
        /// #![feature(nonnull_slice_from_raw_parts)]
        ///
        /// use std::ptr::NonNull;
        ///
        /// // create a slice pointer when starting out with a pointer to the first element
        /// let mut x = [5, 6, 7];
        /// let nonnull_pointer = NonNull::new(x.as_mut_ptr()).unwrap();
        /// let slice = NonNull::slice_from_raw_parts(nonnull_pointer, 3);
        /// assert_eq!(unsafe { slice.as_ref()[2] }, 7);
        /// ```
        ///
        /// (Note that this example artifically demonstrates a use of this method,
        /// but `let slice = NonNull::from(&x[..]);` would be a better way to write code like this.)
        #[unstable(feature = "nonnull_slice_from_raw_parts", issue = "71941")]
        #[rustc_const_unstable(feature = "const_nonnull_slice_from_raw_parts", issue = "71941")]
        #[inline]
        pub const fn slice_from_raw_parts(data: NonNull<T>, len: usize) -> Self {
            // SAFETY: `data` is a `NonNull` pointer which is necessarily non-null
            unsafe { Self::new_unchecked(super::slice_from_raw_parts_mut(data.as_ptr(), len)) }
        }

        /// Returns the length of a non-null raw slice.
        ///
        /// The returned value is the number of **elements**, not the number of bytes.
        ///
        /// This function is safe, even when the non-null raw slice cannot be dereferenced to a slice
        /// because the pointer does not have a valid address.
        ///
        /// # Examples
        ///
        /// ```rust
        /// #![feature(slice_ptr_len, nonnull_slice_from_raw_parts)]
        ///
        /// use std::ptr::NonNull;
        ///
        /// let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
        /// assert_eq!(slice.len(), 3);
        /// ```
        #[unstable(feature = "slice_ptr_len", issue = "71146")]
        #[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")]
        #[inline]
        pub const fn len(self) -> usize {
            self.as_ptr().len()
        }
    }

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> Clone for NonNull<T> {
        #[inline]
        fn clone(&self) -> Self {
            *self
        }
    }

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> Copy for NonNull<T> {}

    #[unstable(feature = "coerce_unsized", issue = "27732")]
    impl<T: ?Sized, U: ?Sized> CoerceUnsized<NonNull<U>> for NonNull<T> where T: Unsize<U> {}

    #[unstable(feature = "dispatch_from_dyn", issue = "none")]
    impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NonNull<U>> for NonNull<T> where T: Unsize<U> {}

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> fmt::Debug for NonNull<T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt::Pointer::fmt(&self.as_ptr(), f)
        }
    }

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> fmt::Pointer for NonNull<T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt::Pointer::fmt(&self.as_ptr(), f)
        }
    }

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> Eq for NonNull<T> {}

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> PartialEq for NonNull<T> {
        #[inline]
        fn eq(&self, other: &Self) -> bool {
            self.as_ptr() == other.as_ptr()
        }
    }

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> Ord for NonNull<T> {
        #[inline]
        fn cmp(&self, other: &Self) -> Ordering {
            self.as_ptr().cmp(&other.as_ptr())
        }
    }

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> PartialOrd for NonNull<T> {
        #[inline]
        fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
            self.as_ptr().partial_cmp(&other.as_ptr())
        }
    }

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> hash::Hash for NonNull<T> {
        #[inline]
        fn hash<H: hash::Hasher>(&self, state: &mut H) {
            self.as_ptr().hash(state)
        }
    }

    #[unstable(feature = "ptr_internals", issue = "none")]
    impl<T: ?Sized> From<Unique<T>> for NonNull<T> {
        #[inline]
        fn from(unique: Unique<T>) -> Self {
            // SAFETY: A Unique pointer cannot be null, so the conditions for
            // new_unchecked() are respected.
            unsafe { NonNull::new_unchecked(unique.as_ptr()) }
        }
    }

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> From<&mut T> for NonNull<T> {
        #[inline]
        fn from(reference: &mut T) -> Self {
            // SAFETY: A mutable reference cannot be null.
            unsafe { NonNull { pointer: reference as *mut T } }
        }
    }

    #[stable(feature = "nonnull", since = "1.25.0")]
    impl<T: ?Sized> From<&T> for NonNull<T> {
        #[inline]
        fn from(reference: &T) -> Self {
            // SAFETY: A reference cannot be null, so the conditions for
            // new_unchecked() are respected.
            unsafe { NonNull { pointer: reference as *const T } }
        }
    }