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| 1 | +use crate::convert::From; |
| 2 | +use crate::ops::{CoerceUnsized, DispatchFromDyn}; |
| 3 | +use crate::fmt; |
| 4 | +use crate::hash; |
| 5 | +use crate::marker::Unsize; |
| 6 | +use crate::mem; |
| 7 | +use crate::ptr::Unique; |
| 8 | +use crate::cmp::Ordering; |
| 9 | + |
| 10 | +/// `*mut T` but non-zero and covariant. |
| 11 | +/// |
| 12 | +/// This is often the correct thing to use when building data structures using |
| 13 | +/// raw pointers, but is ultimately more dangerous to use because of its additional |
| 14 | +/// properties. If you're not sure if you should use `NonNull<T>`, just use `*mut T`! |
| 15 | +/// |
| 16 | +/// Unlike `*mut T`, the pointer must always be non-null, even if the pointer |
| 17 | +/// is never dereferenced. This is so that enums may use this forbidden value |
| 18 | +/// as a discriminant -- `Option<NonNull<T>>` has the same size as `*mut T`. |
| 19 | +/// However the pointer may still dangle if it isn't dereferenced. |
| 20 | +/// |
| 21 | +/// Unlike `*mut T`, `NonNull<T>` is covariant over `T`. If this is incorrect |
| 22 | +/// for your use case, you should include some [`PhantomData`] in your type to |
| 23 | +/// provide invariance, such as `PhantomData<Cell<T>>` or `PhantomData<&'a mut T>`. |
| 24 | +/// Usually this won't be necessary; covariance is correct for most safe abstractions, |
| 25 | +/// such as `Box`, `Rc`, `Arc`, `Vec`, and `LinkedList`. This is the case because they |
| 26 | +/// provide a public API that follows the normal shared XOR mutable rules of Rust. |
| 27 | +/// |
| 28 | +/// Notice that `NonNull<T>` has a `From` instance for `&T`. However, this does |
| 29 | +/// not change the fact that mutating through a (pointer derived from a) shared |
| 30 | +/// reference is undefined behavior unless the mutation happens inside an |
| 31 | +/// [`UnsafeCell<T>`]. The same goes for creating a mutable reference from a shared |
| 32 | +/// reference. When using this `From` instance without an `UnsafeCell<T>`, |
| 33 | +/// it is your responsibility to ensure that `as_mut` is never called, and `as_ptr` |
| 34 | +/// is never used for mutation. |
| 35 | +/// |
| 36 | +/// [`PhantomData`]: ../marker/struct.PhantomData.html |
| 37 | +/// [`UnsafeCell<T>`]: ../cell/struct.UnsafeCell.html |
| 38 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 39 | +#[repr(transparent)] |
| 40 | +#[rustc_layout_scalar_valid_range_start(1)] |
| 41 | +#[cfg_attr(not(stage0), rustc_nonnull_optimization_guaranteed)] |
| 42 | +pub struct NonNull<T: ?Sized> { |
| 43 | + pointer: *const T, |
| 44 | +} |
| 45 | + |
| 46 | +/// `NonNull` pointers are not `Send` because the data they reference may be aliased. |
| 47 | +// N.B., this impl is unnecessary, but should provide better error messages. |
| 48 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 49 | +impl<T: ?Sized> !Send for NonNull<T> { } |
| 50 | + |
| 51 | +/// `NonNull` pointers are not `Sync` because the data they reference may be aliased. |
| 52 | +// N.B., this impl is unnecessary, but should provide better error messages. |
| 53 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 54 | +impl<T: ?Sized> !Sync for NonNull<T> { } |
| 55 | + |
| 56 | +impl<T: Sized> NonNull<T> { |
| 57 | + /// Creates a new `NonNull` that is dangling, but well-aligned. |
| 58 | + /// |
| 59 | + /// This is useful for initializing types which lazily allocate, like |
| 60 | + /// `Vec::new` does. |
| 61 | + /// |
| 62 | + /// Note that the pointer value may potentially represent a valid pointer to |
| 63 | + /// a `T`, which means this must not be used as a "not yet initialized" |
| 64 | + /// sentinel value. Types that lazily allocate must track initialization by |
| 65 | + /// some other means. |
| 66 | + #[stable(feature = "nonnull", since = "1.25.0")] |
| 67 | + #[inline] |
| 68 | + pub const fn dangling() -> Self { |
| 69 | + unsafe { |
| 70 | + let ptr = mem::align_of::<T>() as *mut T; |
| 71 | + NonNull::new_unchecked(ptr) |
| 72 | + } |
| 73 | + } |
| 74 | +} |
| 75 | + |
| 76 | +impl<T: ?Sized> NonNull<T> { |
| 77 | + /// Creates a new `NonNull`. |
| 78 | + /// |
| 79 | + /// # Safety |
| 80 | + /// |
| 81 | + /// `ptr` must be non-null. |
| 82 | + #[stable(feature = "nonnull", since = "1.25.0")] |
| 83 | + #[inline] |
| 84 | + pub const unsafe fn new_unchecked(ptr: *mut T) -> Self { |
| 85 | + NonNull { pointer: ptr as _ } |
| 86 | + } |
| 87 | + |
| 88 | + /// Creates a new `NonNull` if `ptr` is non-null. |
| 89 | + #[stable(feature = "nonnull", since = "1.25.0")] |
| 90 | + #[inline] |
| 91 | + pub fn new(ptr: *mut T) -> Option<Self> { |
| 92 | + if !ptr.is_null() { |
| 93 | + Some(unsafe { Self::new_unchecked(ptr) }) |
| 94 | + } else { |
| 95 | + None |
| 96 | + } |
| 97 | + } |
| 98 | + |
| 99 | + /// Acquires the underlying `*mut` pointer. |
| 100 | + #[stable(feature = "nonnull", since = "1.25.0")] |
| 101 | + #[inline] |
| 102 | + pub const fn as_ptr(self) -> *mut T { |
| 103 | + self.pointer as *mut T |
| 104 | + } |
| 105 | + |
| 106 | + /// Dereferences the content. |
| 107 | + /// |
| 108 | + /// The resulting lifetime is bound to self so this behaves "as if" |
| 109 | + /// it were actually an instance of T that is getting borrowed. If a longer |
| 110 | + /// (unbound) lifetime is needed, use `&*my_ptr.as_ptr()`. |
| 111 | + #[stable(feature = "nonnull", since = "1.25.0")] |
| 112 | + #[inline] |
| 113 | + pub unsafe fn as_ref(&self) -> &T { |
| 114 | + &*self.as_ptr() |
| 115 | + } |
| 116 | + |
| 117 | + /// Mutably dereferences the content. |
| 118 | + /// |
| 119 | + /// The resulting lifetime is bound to self so this behaves "as if" |
| 120 | + /// it were actually an instance of T that is getting borrowed. If a longer |
| 121 | + /// (unbound) lifetime is needed, use `&mut *my_ptr.as_ptr()`. |
| 122 | + #[stable(feature = "nonnull", since = "1.25.0")] |
| 123 | + #[inline] |
| 124 | + pub unsafe fn as_mut(&mut self) -> &mut T { |
| 125 | + &mut *self.as_ptr() |
| 126 | + } |
| 127 | + |
| 128 | + /// Cast to a pointer of another type |
| 129 | + #[stable(feature = "nonnull_cast", since = "1.27.0")] |
| 130 | + #[inline] |
| 131 | + pub const fn cast<U>(self) -> NonNull<U> { |
| 132 | + unsafe { |
| 133 | + NonNull::new_unchecked(self.as_ptr() as *mut U) |
| 134 | + } |
| 135 | + } |
| 136 | +} |
| 137 | + |
| 138 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 139 | +impl<T: ?Sized> Clone for NonNull<T> { |
| 140 | + #[inline] |
| 141 | + fn clone(&self) -> Self { |
| 142 | + *self |
| 143 | + } |
| 144 | +} |
| 145 | + |
| 146 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 147 | +impl<T: ?Sized> Copy for NonNull<T> { } |
| 148 | + |
| 149 | +#[unstable(feature = "coerce_unsized", issue = "27732")] |
| 150 | +impl<T: ?Sized, U: ?Sized> CoerceUnsized<NonNull<U>> for NonNull<T> where T: Unsize<U> { } |
| 151 | + |
| 152 | +#[unstable(feature = "dispatch_from_dyn", issue = "0")] |
| 153 | +impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NonNull<U>> for NonNull<T> where T: Unsize<U> { } |
| 154 | + |
| 155 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 156 | +impl<T: ?Sized> fmt::Debug for NonNull<T> { |
| 157 | + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 158 | + fmt::Pointer::fmt(&self.as_ptr(), f) |
| 159 | + } |
| 160 | +} |
| 161 | + |
| 162 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 163 | +impl<T: ?Sized> fmt::Pointer for NonNull<T> { |
| 164 | + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 165 | + fmt::Pointer::fmt(&self.as_ptr(), f) |
| 166 | + } |
| 167 | +} |
| 168 | + |
| 169 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 170 | +impl<T: ?Sized> Eq for NonNull<T> {} |
| 171 | + |
| 172 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 173 | +impl<T: ?Sized> PartialEq for NonNull<T> { |
| 174 | + #[inline] |
| 175 | + fn eq(&self, other: &Self) -> bool { |
| 176 | + self.as_ptr() == other.as_ptr() |
| 177 | + } |
| 178 | +} |
| 179 | + |
| 180 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 181 | +impl<T: ?Sized> Ord for NonNull<T> { |
| 182 | + #[inline] |
| 183 | + fn cmp(&self, other: &Self) -> Ordering { |
| 184 | + self.as_ptr().cmp(&other.as_ptr()) |
| 185 | + } |
| 186 | +} |
| 187 | + |
| 188 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 189 | +impl<T: ?Sized> PartialOrd for NonNull<T> { |
| 190 | + #[inline] |
| 191 | + fn partial_cmp(&self, other: &Self) -> Option<Ordering> { |
| 192 | + self.as_ptr().partial_cmp(&other.as_ptr()) |
| 193 | + } |
| 194 | +} |
| 195 | + |
| 196 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 197 | +impl<T: ?Sized> hash::Hash for NonNull<T> { |
| 198 | + #[inline] |
| 199 | + fn hash<H: hash::Hasher>(&self, state: &mut H) { |
| 200 | + self.as_ptr().hash(state) |
| 201 | + } |
| 202 | +} |
| 203 | + |
| 204 | +#[unstable(feature = "ptr_internals", issue = "0")] |
| 205 | +impl<T: ?Sized> From<Unique<T>> for NonNull<T> { |
| 206 | + #[inline] |
| 207 | + fn from(unique: Unique<T>) -> Self { |
| 208 | + unsafe { NonNull::new_unchecked(unique.as_ptr()) } |
| 209 | + } |
| 210 | +} |
| 211 | + |
| 212 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 213 | +impl<T: ?Sized> From<&mut T> for NonNull<T> { |
| 214 | + #[inline] |
| 215 | + fn from(reference: &mut T) -> Self { |
| 216 | + unsafe { NonNull { pointer: reference as *mut T } } |
| 217 | + } |
| 218 | +} |
| 219 | + |
| 220 | +#[stable(feature = "nonnull", since = "1.25.0")] |
| 221 | +impl<T: ?Sized> From<&T> for NonNull<T> { |
| 222 | + #[inline] |
| 223 | + fn from(reference: &T) -> Self { |
| 224 | + unsafe { NonNull { pointer: reference as *const T } } |
| 225 | + } |
| 226 | +} |
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