Type Alias makepad_objc_sys::runtime::ObjcId

source · 
pub type ObjcId = *mut Object;

Implementations§

source§

impl<T> *mut Twhere T: ?Sized,

1.0.0 (const: unstable) · source

pub fn is_null(self) -> bool

Returns true if the pointer is null.

Note that unsized types have many possible null pointers, as only the raw data pointer is considered, not their length, vtable, etc. Therefore, two pointers that are null may still not compare equal to each other.

Behavior during const evaluation

When this function is used during const evaluation, it may return false for pointers that turn out to be null at runtime. Specifically, when a pointer to some memory is offset beyond its bounds in such a way that the resulting pointer is null, the function will still return false. There is no way for CTFE to know the absolute position of that memory, so we cannot tell if the pointer is null or not.

Examples
let mut s = [1, 2, 3];
let ptr: *mut u32 = s.as_mut_ptr();
assert!(!ptr.is_null());
1.38.0 (const: 1.38.0) · source

pub const fn cast<U>(self) -> *mut U

Casts to a pointer of another type.

const: unstable · source

pub fn with_metadata_of<U>(self, meta: *const U) -> *mut Uwhere U: ?Sized,

🔬This is a nightly-only experimental API. (set_ptr_value)

Use the pointer value in a new pointer of another type.

In case meta is a (fat) pointer to an unsized type, this operation will ignore the pointer part, whereas for (thin) pointers to sized types, this has the same effect as a simple cast.

The resulting pointer will have provenance of self, i.e., for a fat pointer, this operation is semantically the same as creating a new fat pointer with the data pointer value of self but the metadata of meta.

Examples

This function is primarily useful for allowing byte-wise pointer arithmetic on potentially fat pointers:

#![feature(set_ptr_value)]
let mut arr: [i32; 3] = [1, 2, 3];
let mut ptr = arr.as_mut_ptr() as *mut dyn Debug;
let thin = ptr as *mut u8;
unsafe {
    ptr = thin.add(8).with_metadata_of(ptr);
    println!("{:?}", &*ptr); // will print "3"
}
1.65.0 (const: 1.65.0) · source

pub const fn cast_const(self) -> *const T

Changes constness without changing the type.

This is a bit safer than as because it wouldn’t silently change the type if the code is refactored.

While not strictly required (*mut T coerces to *const T), this is provided for symmetry with cast_mut on *const T and may have documentation value if used instead of implicit coercion.

source

pub fn to_bits(self) -> usize

👎Deprecated since 1.67.0: replaced by the expose_addr method, or update your code to follow the strict provenance rules using its APIs
🔬This is a nightly-only experimental API. (ptr_to_from_bits)

Casts a pointer to its raw bits.

This is equivalent to as usize, but is more specific to enhance readability. The inverse method is from_bits.

In particular, *p as usize and p as usize will both compile for pointers to numeric types but do very different things, so using this helps emphasize that reading the bits was intentional.

Examples
#![feature(ptr_to_from_bits)]
let mut array = [13, 42];
let mut it = array.iter_mut();
let p0: *mut i32 = it.next().unwrap();
assert_eq!(<*mut _>::from_bits(p0.to_bits()), p0);
let p1: *mut i32 = it.next().unwrap();
assert_eq!(p1.to_bits() - p0.to_bits(), 4);
}
source

pub fn from_bits(bits: usize) -> *mut T

👎Deprecated since 1.67.0: replaced by the ptr::from_exposed_addr_mut function, or update your code to follow the strict provenance rules using its APIs
🔬This is a nightly-only experimental API. (ptr_to_from_bits)

Creates a pointer from its raw bits.

This is equivalent to as *mut T, but is more specific to enhance readability. The inverse method is to_bits.

Examples
#![feature(ptr_to_from_bits)]
use std::ptr::NonNull;
let dangling: *mut u8 = NonNull::dangling().as_ptr();
assert_eq!(<*mut u8>::from_bits(1), dangling);
}
source

pub fn addr(self) -> usize

🔬This is a nightly-only experimental API. (strict_provenance)

Gets the “address” portion of the pointer.

This is similar to self as usize, which semantically discards provenance and address-space information. However, unlike self as usize, casting the returned address back to a pointer yields invalid, which is undefined behavior to dereference. To properly restore the lost information and obtain a dereferenceable pointer, use with_addr or map_addr.

If using those APIs is not possible because there is no way to preserve a pointer with the required provenance, use expose_addr and from_exposed_addr_mut instead. However, note that this makes your code less portable and less amenable to tools that check for compliance with the Rust memory model.

On most platforms this will produce a value with the same bytes as the original pointer, because all the bytes are dedicated to describing the address. Platforms which need to store additional information in the pointer may perform a change of representation to produce a value containing only the address portion of the pointer. What that means is up to the platform to define.

This API and its claimed semantics are part of the Strict Provenance experiment, and as such might change in the future (including possibly weakening this so it becomes wholly equivalent to self as usize). See the module documentation for details.

source

pub fn expose_addr(self) -> usize

🔬This is a nightly-only experimental API. (strict_provenance)

Gets the “address” portion of the pointer, and ‘exposes’ the “provenance” part for future use in from_exposed_addr.

This is equivalent to self as usize, which semantically discards provenance and address-space information. Furthermore, this (like the as cast) has the implicit side-effect of marking the provenance as ‘exposed’, so on platforms that support it you can later call from_exposed_addr_mut to reconstitute the original pointer including its provenance. (Reconstructing address space information, if required, is your responsibility.)

Using this method means that code is not following Strict Provenance rules. Supporting from_exposed_addr_mut complicates specification and reasoning and may not be supported by tools that help you to stay conformant with the Rust memory model, so it is recommended to use addr wherever possible.

On most platforms this will produce a value with the same bytes as the original pointer, because all the bytes are dedicated to describing the address. Platforms which need to store additional information in the pointer may not support this operation, since the ‘expose’ side-effect which is required for from_exposed_addr_mut to work is typically not available.

This API and its claimed semantics are part of the Strict Provenance experiment, see the module documentation for details.

source

pub fn with_addr(self, addr: usize) -> *mut T

🔬This is a nightly-only experimental API. (strict_provenance)

Creates a new pointer with the given address.

This performs the same operation as an addr as ptr cast, but copies the address-space and provenance of self to the new pointer. This allows us to dynamically preserve and propagate this important information in a way that is otherwise impossible with a unary cast.

This is equivalent to using wrapping_offset to offset self to the given address, and therefore has all the same capabilities and restrictions.

This API and its claimed semantics are part of the Strict Provenance experiment, see the module documentation for details.

source

pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> *mut T

🔬This is a nightly-only experimental API. (strict_provenance)

Creates a new pointer by mapping self’s address to a new one.

This is a convenience for with_addr, see that method for details.

This API and its claimed semantics are part of the Strict Provenance experiment, see the module documentation for details.

const: unstable · source

pub fn to_raw_parts(self) -> (*mut (), <T as Pointee>::Metadata)

🔬This is a nightly-only experimental API. (ptr_metadata)

Decompose a (possibly wide) pointer into its address and metadata components.

The pointer can be later reconstructed with from_raw_parts_mut.

1.9.0 (const: unstable) · source

pub unsafe fn as_ref<'a>(self) -> Option<&'a T>

Returns None if the pointer is null, or else returns a shared reference to the value wrapped in Some. If the value may be uninitialized, as_uninit_ref must be used instead.

For the mutable counterpart see as_mut.

Safety

When calling this method, you have to ensure that either the pointer is null or all of the following is true:

  • The pointer must be properly aligned.

  • It must be “dereferenceable” in the sense defined in the module documentation.

  • The pointer must point to an initialized instance of T.

  • You must enforce Rust’s aliasing rules, since the returned lifetime 'a is arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. In particular, while this reference exists, the memory the pointer points to must not get mutated (except inside UnsafeCell).

This applies even if the result of this method is unused! (The part about being initialized is not yet fully decided, but until it is, the only safe approach is to ensure that they are indeed initialized.)

Examples
let ptr: *mut u8 = &mut 10u8 as *mut u8;

unsafe {
    if let Some(val_back) = ptr.as_ref() {
        println!("We got back the value: {val_back}!");
    }
}
Null-unchecked version

If you are sure the pointer can never be null and are looking for some kind of as_ref_unchecked that returns the &T instead of Option<&T>, know that you can dereference the pointer directly.

let ptr: *mut u8 = &mut 10u8 as *mut u8;

unsafe {
    let val_back = &*ptr;
    println!("We got back the value: {val_back}!");
}
const: unstable · source

pub unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>

🔬This is a nightly-only experimental API. (ptr_as_uninit)

Returns None if the pointer is null, or else returns a shared reference to the value wrapped in Some. In contrast to as_ref, this does not require that the value has to be initialized.

For the mutable counterpart see as_uninit_mut.

Safety

When calling this method, you have to ensure that either the pointer is null or all of the following is true:

  • The pointer must be properly aligned.

  • It must be “dereferenceable” in the sense defined in the module documentation.

  • You must enforce Rust’s aliasing rules, since the returned lifetime 'a is arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. In particular, while this reference exists, the memory the pointer points to must not get mutated (except inside UnsafeCell).

This applies even if the result of this method is unused!

Examples
#![feature(ptr_as_uninit)]

let ptr: *mut u8 = &mut 10u8 as *mut u8;

unsafe {
    if let Some(val_back) = ptr.as_uninit_ref() {
        println!("We got back the value: {}!", val_back.assume_init());
    }
}
1.0.0 (const: 1.61.0) · source

pub const unsafe fn offset(self, count: isize) -> *mut T

Calculates the offset from a pointer.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

Safety

If any of the following conditions are violated, the result is Undefined Behavior:

  • Both the starting and resulting pointer must be either in bounds or one byte past the end of the same allocated object.

  • The computed offset, in bytes, cannot overflow an isize.

  • The offset being in bounds cannot rely on “wrapping around” the address space. That is, the infinite-precision sum, in bytes must fit in a usize.

The compiler and standard library generally tries to ensure allocations never reach a size where an offset is a concern. For instance, Vec and Box ensure they never allocate more than isize::MAX bytes, so vec.as_ptr().add(vec.len()) is always safe.

Most platforms fundamentally can’t even construct such an allocation. For instance, no known 64-bit platform can ever serve a request for 263 bytes due to page-table limitations or splitting the address space. However, some 32-bit and 16-bit platforms may successfully serve a request for more than isize::MAX bytes with things like Physical Address Extension. As such, memory acquired directly from allocators or memory mapped files may be too large to handle with this function.

Consider using wrapping_offset instead if these constraints are difficult to satisfy. The only advantage of this method is that it enables more aggressive compiler optimizations.

Examples
let mut s = [1, 2, 3];
let ptr: *mut u32 = s.as_mut_ptr();

unsafe {
    println!("{}", *ptr.offset(1));
    println!("{}", *ptr.offset(2));
}
const: unstable · source

pub unsafe fn byte_offset(self, count: isize) -> *mut T

🔬This is a nightly-only experimental API. (pointer_byte_offsets)

Calculates the offset from a pointer in bytes.

count is in units of bytes.

This is purely a convenience for casting to a u8 pointer and using offset on it. See that method for documentation and safety requirements.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

1.16.0 (const: 1.61.0) · source

pub const fn wrapping_offset(self, count: isize) -> *mut T

Calculates the offset from a pointer using wrapping arithmetic. count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

Safety

This operation itself is always safe, but using the resulting pointer is not.

The resulting pointer “remembers” the allocated object that self points to; it must not be used to read or write other allocated objects.

In other words, let z = x.wrapping_offset((y as isize) - (x as isize)) does not make z the same as y even if we assume T has size 1 and there is no overflow: z is still attached to the object x is attached to, and dereferencing it is Undefined Behavior unless x and y point into the same allocated object.

Compared to offset, this method basically delays the requirement of staying within the same allocated object: offset is immediate Undefined Behavior when crossing object boundaries; wrapping_offset produces a pointer but still leads to Undefined Behavior if a pointer is dereferenced when it is out-of-bounds of the object it is attached to. offset can be optimized better and is thus preferable in performance-sensitive code.

The delayed check only considers the value of the pointer that was dereferenced, not the intermediate values used during the computation of the final result. For example, x.wrapping_offset(o).wrapping_offset(o.wrapping_neg()) is always the same as x. In other words, leaving the allocated object and then re-entering it later is permitted.

Examples
// Iterate using a raw pointer in increments of two elements
let mut data = [1u8, 2, 3, 4, 5];
let mut ptr: *mut u8 = data.as_mut_ptr();
let step = 2;
let end_rounded_up = ptr.wrapping_offset(6);

while ptr != end_rounded_up {
    unsafe {
        *ptr = 0;
    }
    ptr = ptr.wrapping_offset(step);
}
assert_eq!(&data, &[0, 2, 0, 4, 0]);
const: unstable · source

pub fn wrapping_byte_offset(self, count: isize) -> *mut T

🔬This is a nightly-only experimental API. (pointer_byte_offsets)

Calculates the offset from a pointer in bytes using wrapping arithmetic.

count is in units of bytes.

This is purely a convenience for casting to a u8 pointer and using wrapping_offset on it. See that method for documentation.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

source

pub fn mask(self, mask: usize) -> *mut T

🔬This is a nightly-only experimental API. (ptr_mask)

Masks out bits of the pointer according to a mask.

This is convenience for ptr.map_addr(|a| a & mask).

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

Examples
#![feature(ptr_mask, strict_provenance)]
let mut v = 17_u32;
let ptr: *mut u32 = &mut v;

// `u32` is 4 bytes aligned,
// which means that lower 2 bits are always 0.
let tag_mask = 0b11;
let ptr_mask = !tag_mask;

// We can store something in these lower bits
let tagged_ptr = ptr.map_addr(|a| a | 0b10);

// Get the "tag" back
let tag = tagged_ptr.addr() & tag_mask;
assert_eq!(tag, 0b10);

// Note that `tagged_ptr` is unaligned, it's UB to read from/write to it.
// To get original pointer `mask` can be used:
let masked_ptr = tagged_ptr.mask(ptr_mask);
assert_eq!(unsafe { *masked_ptr }, 17);

unsafe { *masked_ptr = 0 };
assert_eq!(v, 0);
1.9.0 (const: unstable) · source

pub unsafe fn as_mut<'a>(self) -> Option<&'a mut T>

Returns None if the pointer is null, or else returns a unique reference to the value wrapped in Some. If the value may be uninitialized, as_uninit_mut must be used instead.

For the shared counterpart see as_ref.

Safety

When calling this method, you have to ensure that either the pointer is null or all of the following is true:

  • The pointer must be properly aligned.

  • It must be “dereferenceable” in the sense defined in the module documentation.

  • The pointer must point to an initialized instance of T.

  • You must enforce Rust’s aliasing rules, since the returned lifetime 'a is arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. In particular, while this reference exists, the memory the pointer points to must not get accessed (read or written) through any other pointer.

This applies even if the result of this method is unused! (The part about being initialized is not yet fully decided, but until it is, the only safe approach is to ensure that they are indeed initialized.)

Examples
let mut s = [1, 2, 3];
let ptr: *mut u32 = s.as_mut_ptr();
let first_value = unsafe { ptr.as_mut().unwrap() };
*first_value = 4;
println!("{s:?}"); // It'll print: "[4, 2, 3]".
Null-unchecked version

If you are sure the pointer can never be null and are looking for some kind of as_mut_unchecked that returns the &mut T instead of Option<&mut T>, know that you can dereference the pointer directly.

let mut s = [1, 2, 3];
let ptr: *mut u32 = s.as_mut_ptr();
let first_value = unsafe { &mut *ptr };
*first_value = 4;
println!("{s:?}"); // It'll print: "[4, 2, 3]".
const: unstable · source

pub unsafe fn as_uninit_mut<'a>(self) -> Option<&'a mut MaybeUninit<T>>

🔬This is a nightly-only experimental API. (ptr_as_uninit)

Returns None if the pointer is null, or else returns a unique reference to the value wrapped in Some. In contrast to as_mut, this does not require that the value has to be initialized.

For the shared counterpart see as_uninit_ref.

Safety

When calling this method, you have to ensure that either the pointer is null or all of the following is true:

  • The pointer must be properly aligned.

  • It must be “dereferenceable” in the sense defined in the module documentation.

  • You must enforce Rust’s aliasing rules, since the returned lifetime 'a is arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. In particular, while this reference exists, the memory the pointer points to must not get accessed (read or written) through any other pointer.

This applies even if the result of this method is unused!

const: unstable · source

pub fn guaranteed_eq(self, other: *mut T) -> Option<bool>

🔬This is a nightly-only experimental API. (const_raw_ptr_comparison)

Returns whether two pointers are guaranteed to be equal.

At runtime this function behaves like Some(self == other). However, in some contexts (e.g., compile-time evaluation), it is not always possible to determine equality of two pointers, so this function may spuriously return None for pointers that later actually turn out to have its equality known. But when it returns Some, the pointers’ equality is guaranteed to be known.

The return value may change from Some to None and vice versa depending on the compiler version and unsafe code must not rely on the result of this function for soundness. It is suggested to only use this function for performance optimizations where spurious None return values by this function do not affect the outcome, but just the performance. The consequences of using this method to make runtime and compile-time code behave differently have not been explored. This method should not be used to introduce such differences, and it should also not be stabilized before we have a better understanding of this issue.

const: unstable · source

pub fn guaranteed_ne(self, other: *mut T) -> Option<bool>

🔬This is a nightly-only experimental API. (const_raw_ptr_comparison)

Returns whether two pointers are guaranteed to be inequal.

At runtime this function behaves like Some(self != other). However, in some contexts (e.g., compile-time evaluation), it is not always possible to determine inequality of two pointers, so this function may spuriously return None for pointers that later actually turn out to have its inequality known. But when it returns Some, the pointers’ inequality is guaranteed to be known.

The return value may change from Some to None and vice versa depending on the compiler version and unsafe code must not rely on the result of this function for soundness. It is suggested to only use this function for performance optimizations where spurious None return values by this function do not affect the outcome, but just the performance. The consequences of using this method to make runtime and compile-time code behave differently have not been explored. This method should not be used to introduce such differences, and it should also not be stabilized before we have a better understanding of this issue.

1.47.0 (const: 1.65.0) · source

pub const unsafe fn offset_from(self, origin: *const T) -> isize

Calculates the distance between two pointers. The returned value is in units of T: the distance in bytes divided by mem::size_of::<T>().

This function is the inverse of offset.

Safety

If any of the following conditions are violated, the result is Undefined Behavior:

  • Both the starting and other pointer must be either in bounds or one byte past the end of the same allocated object.

  • Both pointers must be derived from a pointer to the same object. (See below for an example.)

  • The distance between the pointers, in bytes, must be an exact multiple of the size of T.

  • The distance between the pointers, in bytes, cannot overflow an isize.

  • The distance being in bounds cannot rely on “wrapping around” the address space.

Rust types are never larger than isize::MAX and Rust allocations never wrap around the address space, so two pointers within some value of any Rust type T will always satisfy the last two conditions. The standard library also generally ensures that allocations never reach a size where an offset is a concern. For instance, Vec and Box ensure they never allocate more than isize::MAX bytes, so ptr_into_vec.offset_from(vec.as_ptr()) always satisfies the last two conditions.

Most platforms fundamentally can’t even construct such a large allocation. For instance, no known 64-bit platform can ever serve a request for 263 bytes due to page-table limitations or splitting the address space. However, some 32-bit and 16-bit platforms may successfully serve a request for more than isize::MAX bytes with things like Physical Address Extension. As such, memory acquired directly from allocators or memory mapped files may be too large to handle with this function. (Note that offset and add also have a similar limitation and hence cannot be used on such large allocations either.)

Panics

This function panics if T is a Zero-Sized Type (“ZST”).

Examples

Basic usage:

let mut a = [0; 5];
let ptr1: *mut i32 = &mut a[1];
let ptr2: *mut i32 = &mut a[3];
unsafe {
    assert_eq!(ptr2.offset_from(ptr1), 2);
    assert_eq!(ptr1.offset_from(ptr2), -2);
    assert_eq!(ptr1.offset(2), ptr2);
    assert_eq!(ptr2.offset(-2), ptr1);
}

Incorrect usage:

let ptr1 = Box::into_raw(Box::new(0u8));
let ptr2 = Box::into_raw(Box::new(1u8));
let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize);
// Make ptr2_other an "alias" of ptr2, but derived from ptr1.
let ptr2_other = (ptr1 as *mut u8).wrapping_offset(diff);
assert_eq!(ptr2 as usize, ptr2_other as usize);
// Since ptr2_other and ptr2 are derived from pointers to different objects,
// computing their offset is undefined behavior, even though
// they point to the same address!
unsafe {
    let zero = ptr2_other.offset_from(ptr2); // Undefined Behavior
}
const: unstable · source

pub unsafe fn byte_offset_from<U>(self, origin: *const U) -> isizewhere U: ?Sized,

🔬This is a nightly-only experimental API. (pointer_byte_offsets)

Calculates the distance between two pointers. The returned value is in units of bytes.

This is purely a convenience for casting to a u8 pointer and using offset_from on it. See that method for documentation and safety requirements.

For non-Sized pointees this operation considers only the data pointers, ignoring the metadata.

const: unstable · source

pub unsafe fn sub_ptr(self, origin: *const T) -> usize

🔬This is a nightly-only experimental API. (ptr_sub_ptr)

Calculates the distance between two pointers, where it’s known that self is equal to or greater than origin. The returned value is in units of T: the distance in bytes is divided by mem::size_of::<T>().

This computes the same value that offset_from would compute, but with the added precondition that the offset is guaranteed to be non-negative. This method is equivalent to usize::try_from(self.offset_from(origin)).unwrap_unchecked(), but it provides slightly more information to the optimizer, which can sometimes allow it to optimize slightly better with some backends.

This method can be though of as recovering the count that was passed to add (or, with the parameters in the other order, to sub). The following are all equivalent, assuming that their safety preconditions are met:

ptr.sub_ptr(origin) == count
origin.add(count) == ptr
ptr.sub(count) == origin
Safety

  • The distance between the pointers must be non-negative (self >= origin)

  • All the safety conditions of offset_from apply to this method as well; see it for the full details.

Importantly, despite the return type of this method being able to represent a larger offset, it’s still not permitted to pass pointers which differ by more than isize::MAX bytes. As such, the result of this method will always be less than or equal to isize::MAX as usize.

Panics

This function panics if T is a Zero-Sized Type (“ZST”).

Examples
#![feature(ptr_sub_ptr)]

let mut a = [0; 5];
let p: *mut i32 = a.as_mut_ptr();
unsafe {
    let ptr1: *mut i32 = p.add(1);
    let ptr2: *mut i32 = p.add(3);

    assert_eq!(ptr2.sub_ptr(ptr1), 2);
    assert_eq!(ptr1.add(2), ptr2);
    assert_eq!(ptr2.sub(2), ptr1);
    assert_eq!(ptr2.sub_ptr(ptr2), 0);
}

// This would be incorrect, as the pointers are not correctly ordered:
// ptr1.offset_from(ptr2)
1.26.0 (const: 1.61.0) · source

pub const unsafe fn add(self, count: usize) -> *mut T

Calculates the offset from a pointer (convenience for .offset(count as isize)).

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

Safety

If any of the following conditions are violated, the result is Undefined Behavior:

  • Both the starting and resulting pointer must be either in bounds or one byte past the end of the same allocated object.

  • The computed offset, in bytes, cannot overflow an isize.

  • The offset being in bounds cannot rely on “wrapping around” the address space. That is, the infinite-precision sum must fit in a usize.

The compiler and standard library generally tries to ensure allocations never reach a size where an offset is a concern. For instance, Vec and Box ensure they never allocate more than isize::MAX bytes, so vec.as_ptr().add(vec.len()) is always safe.

Most platforms fundamentally can’t even construct such an allocation. For instance, no known 64-bit platform can ever serve a request for 263 bytes due to page-table limitations or splitting the address space. However, some 32-bit and 16-bit platforms may successfully serve a request for more than isize::MAX bytes with things like Physical Address Extension. As such, memory acquired directly from allocators or memory mapped files may be too large to handle with this function.

Consider using wrapping_add instead if these constraints are difficult to satisfy. The only advantage of this method is that it enables more aggressive compiler optimizations.

Examples
let s: &str = "123";
let ptr: *const u8 = s.as_ptr();

unsafe {
    println!("{}", *ptr.add(1) as char);
    println!("{}", *ptr.add(2) as char);
}
const: unstable · source

pub unsafe fn byte_add(self, count: usize) -> *mut T

🔬This is a nightly-only experimental API. (pointer_byte_offsets)

Calculates the offset from a pointer in bytes (convenience for .byte_offset(count as isize)).

count is in units of bytes.

This is purely a convenience for casting to a u8 pointer and using add on it. See that method for documentation and safety requirements.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

1.26.0 (const: 1.61.0) · source

pub const unsafe fn sub(self, count: usize) -> *mut T

Calculates the offset from a pointer (convenience for .offset((count as isize).wrapping_neg())).

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

Safety

If any of the following conditions are violated, the result is Undefined Behavior:

  • Both the starting and resulting pointer must be either in bounds or one byte past the end of the same allocated object.

  • The computed offset cannot exceed isize::MAX bytes.

  • The offset being in bounds cannot rely on “wrapping around” the address space. That is, the infinite-precision sum must fit in a usize.

The compiler and standard library generally tries to ensure allocations never reach a size where an offset is a concern. For instance, Vec and Box ensure they never allocate more than isize::MAX bytes, so vec.as_ptr().add(vec.len()).sub(vec.len()) is always safe.

Most platforms fundamentally can’t even construct such an allocation. For instance, no known 64-bit platform can ever serve a request for 263 bytes due to page-table limitations or splitting the address space. However, some 32-bit and 16-bit platforms may successfully serve a request for more than isize::MAX bytes with things like Physical Address Extension. As such, memory acquired directly from allocators or memory mapped files may be too large to handle with this function.

Consider using wrapping_sub instead if these constraints are difficult to satisfy. The only advantage of this method is that it enables more aggressive compiler optimizations.

Examples
let s: &str = "123";

unsafe {
    let end: *const u8 = s.as_ptr().add(3);
    println!("{}", *end.sub(1) as char);
    println!("{}", *end.sub(2) as char);
}
const: unstable · source

pub unsafe fn byte_sub(self, count: usize) -> *mut T

🔬This is a nightly-only experimental API. (pointer_byte_offsets)

Calculates the offset from a pointer in bytes (convenience for .byte_offset((count as isize).wrapping_neg())).

count is in units of bytes.

This is purely a convenience for casting to a u8 pointer and using sub on it. See that method for documentation and safety requirements.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

1.26.0 (const: 1.61.0) · source

pub const fn wrapping_add(self, count: usize) -> *mut T

Calculates the offset from a pointer using wrapping arithmetic. (convenience for .wrapping_offset(count as isize))

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

Safety

This operation itself is always safe, but using the resulting pointer is not.

The resulting pointer “remembers” the allocated object that self points to; it must not be used to read or write other allocated objects.

In other words, let z = x.wrapping_add((y as usize) - (x as usize)) does not make z the same as y even if we assume T has size 1 and there is no overflow: z is still attached to the object x is attached to, and dereferencing it is Undefined Behavior unless x and y point into the same allocated object.

Compared to add, this method basically delays the requirement of staying within the same allocated object: add is immediate Undefined Behavior when crossing object boundaries; wrapping_add produces a pointer but still leads to Undefined Behavior if a pointer is dereferenced when it is out-of-bounds of the object it is attached to. add can be optimized better and is thus preferable in performance-sensitive code.

The delayed check only considers the value of the pointer that was dereferenced, not the intermediate values used during the computation of the final result. For example, x.wrapping_add(o).wrapping_sub(o) is always the same as x. In other words, leaving the allocated object and then re-entering it later is permitted.

Examples
// Iterate using a raw pointer in increments of two elements
let data = [1u8, 2, 3, 4, 5];
let mut ptr: *const u8 = data.as_ptr();
let step = 2;
let end_rounded_up = ptr.wrapping_add(6);

// This loop prints "1, 3, 5, "
while ptr != end_rounded_up {
    unsafe {
        print!("{}, ", *ptr);
    }
    ptr = ptr.wrapping_add(step);
}
const: unstable · source

pub fn wrapping_byte_add(self, count: usize) -> *mut T

🔬This is a nightly-only experimental API. (pointer_byte_offsets)

Calculates the offset from a pointer in bytes using wrapping arithmetic. (convenience for .wrapping_byte_offset(count as isize))

count is in units of bytes.

This is purely a convenience for casting to a u8 pointer and using wrapping_add on it. See that method for documentation.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

1.26.0 (const: 1.61.0) · source

pub const fn wrapping_sub(self, count: usize) -> *mut T

Calculates the offset from a pointer using wrapping arithmetic. (convenience for .wrapping_offset((count as isize).wrapping_neg()))

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

Safety

This operation itself is always safe, but using the resulting pointer is not.

The resulting pointer “remembers” the allocated object that self points to; it must not be used to read or write other allocated objects.

In other words, let z = x.wrapping_sub((x as usize) - (y as usize)) does not make z the same as y even if we assume T has size 1 and there is no overflow: z is still attached to the object x is attached to, and dereferencing it is Undefined Behavior unless x and y point into the same allocated object.

Compared to sub, this method basically delays the requirement of staying within the same allocated object: sub is immediate Undefined Behavior when crossing object boundaries; wrapping_sub produces a pointer but still leads to Undefined Behavior if a pointer is dereferenced when it is out-of-bounds of the object it is attached to. sub can be optimized better and is thus preferable in performance-sensitive code.

The delayed check only considers the value of the pointer that was dereferenced, not the intermediate values used during the computation of the final result. For example, x.wrapping_add(o).wrapping_sub(o) is always the same as x. In other words, leaving the allocated object and then re-entering it later is permitted.

Examples
// Iterate using a raw pointer in increments of two elements (backwards)
let data = [1u8, 2, 3, 4, 5];
let mut ptr: *const u8 = data.as_ptr();
let start_rounded_down = ptr.wrapping_sub(2);
ptr = ptr.wrapping_add(4);
let step = 2;
// This loop prints "5, 3, 1, "
while ptr != start_rounded_down {
    unsafe {
        print!("{}, ", *ptr);
    }
    ptr = ptr.wrapping_sub(step);
}
const: unstable · source

pub fn wrapping_byte_sub(self, count: usize) -> *mut T

🔬This is a nightly-only experimental API. (pointer_byte_offsets)

Calculates the offset from a pointer in bytes using wrapping arithmetic. (convenience for .wrapping_offset((count as isize).wrapping_neg()))

count is in units of bytes.

This is purely a convenience for casting to a u8 pointer and using wrapping_sub on it. See that method for documentation.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

1.26.0 (const: 1.71.0) · source

pub const unsafe fn read(self) -> T

Reads the value from self without moving it. This leaves the memory in self unchanged.

See ptr::read for safety concerns and examples.

1.26.0 · source

pub unsafe fn read_volatile(self) -> T

Performs a volatile read of the value from self without moving it. This leaves the memory in self unchanged.

Volatile operations are intended to act on I/O memory, and are guaranteed to not be elided or reordered by the compiler across other volatile operations.

See ptr::read_volatile for safety concerns and examples.

1.26.0 (const: 1.71.0) · source

pub const unsafe fn read_unaligned(self) -> T

Reads the value from self without moving it. This leaves the memory in self unchanged.

Unlike read, the pointer may be unaligned.

See ptr::read_unaligned for safety concerns and examples.

1.26.0 (const: 1.63.0) · source

pub const unsafe fn copy_to(self, dest: *mut T, count: usize)

Copies count * size_of<T> bytes from self to dest. The source and destination may overlap.

NOTE: this has the same argument order as ptr::copy.

See ptr::copy for safety concerns and examples.

1.26.0 (const: 1.63.0) · source

pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize)

Copies count * size_of<T> bytes from self to dest. The source and destination may not overlap.

NOTE: this has the same argument order as ptr::copy_nonoverlapping.

See ptr::copy_nonoverlapping for safety concerns and examples.

1.26.0 (const: 1.63.0) · source

pub const unsafe fn copy_from(self, src: *const T, count: usize)

Copies count * size_of<T> bytes from src to self. The source and destination may overlap.

NOTE: this has the opposite argument order of ptr::copy.

See ptr::copy for safety concerns and examples.

1.26.0 (const: 1.63.0) · source

pub const unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize)

Copies count * size_of<T> bytes from src to self. The source and destination may not overlap.

NOTE: this has the opposite argument order of ptr::copy_nonoverlapping.

See ptr::copy_nonoverlapping for safety concerns and examples.

1.26.0 · source

pub unsafe fn drop_in_place(self)

Executes the destructor (if any) of the pointed-to value.

See ptr::drop_in_place for safety concerns and examples.

1.26.0 (const: unstable) · source

pub unsafe fn write(self, val: T)

Overwrites a memory location with the given value without reading or dropping the old value.

See ptr::write for safety concerns and examples.

1.26.0 (const: unstable) · source

pub unsafe fn write_bytes(self, val: u8, count: usize)

Invokes memset on the specified pointer, setting count * size_of::<T>() bytes of memory starting at self to val.

See ptr::write_bytes for safety concerns and examples.

1.26.0 · source

pub unsafe fn write_volatile(self, val: T)

Performs a volatile write of a memory location with the given value without reading or dropping the old value.

Volatile operations are intended to act on I/O memory, and are guaranteed to not be elided or reordered by the compiler across other volatile operations.

See ptr::write_volatile for safety concerns and examples.

1.26.0 (const: unstable) · source

pub unsafe fn write_unaligned(self, val: T)

Overwrites a memory location with the given value without reading or dropping the old value.

Unlike write, the pointer may be unaligned.

See ptr::write_unaligned for safety concerns and examples.

1.26.0 · source

pub unsafe fn replace(self, src: T) -> T

Replaces the value at self with src, returning the old value, without dropping either.

See ptr::replace for safety concerns and examples.

1.26.0 (const: unstable) · source

pub unsafe fn swap(self, with: *mut T)

Swaps the values at two mutable locations of the same type, without deinitializing either. They may overlap, unlike mem::swap which is otherwise equivalent.

See ptr::swap for safety concerns and examples.

1.36.0 (const: unstable) · source

pub fn align_offset(self, align: usize) -> usize

Computes the offset that needs to be applied to the pointer in order to make it aligned to align.

If it is not possible to align the pointer, the implementation returns usize::MAX. It is permissible for the implementation to always return usize::MAX. Only your algorithm’s performance can depend on getting a usable offset here, not its correctness.

The offset is expressed in number of T elements, and not bytes. The value returned can be used with the wrapping_add method.

There are no guarantees whatsoever that offsetting the pointer will not overflow or go beyond the allocation that the pointer points into. It is up to the caller to ensure that the returned offset is correct in all terms other than alignment.

Panics

The function panics if align is not a power-of-two.

Examples

Accessing adjacent u8 as u16

use std::mem::align_of;

let mut x = [5_u8, 6, 7, 8, 9];
let ptr = x.as_mut_ptr();
let offset = ptr.align_offset(align_of::<u16>());

if offset < x.len() - 1 {
    let u16_ptr = ptr.add(offset).cast::<u16>();
    *u16_ptr = 0;

    assert!(x == [0, 0, 7, 8, 9] || x == [5, 0, 0, 8, 9]);
} else {
    // while the pointer can be aligned via `offset`, it would point
    // outside the allocation
}
const: unstable · source

pub fn is_aligned(self) -> bool

🔬This is a nightly-only experimental API. (pointer_is_aligned)

Returns whether the pointer is properly aligned for T.

Examples
#![feature(pointer_is_aligned)]
#![feature(pointer_byte_offsets)]

// On some platforms, the alignment of i32 is less than 4.
#[repr(align(4))]
struct AlignedI32(i32);

let mut data = AlignedI32(42);
let ptr = &mut data as *mut AlignedI32;

assert!(ptr.is_aligned());
assert!(!ptr.wrapping_byte_add(1).is_aligned());
At compiletime

Note: Alignment at compiletime is experimental and subject to change. See the tracking issue for details.

At compiletime, the compiler may not know where a value will end up in memory. Calling this function on a pointer created from a reference at compiletime will only return true if the pointer is guaranteed to be aligned. This means that the pointer is never aligned if cast to a type with a stricter alignment than the reference’s underlying allocation.

#![feature(pointer_is_aligned)]
#![feature(const_pointer_is_aligned)]
#![feature(const_mut_refs)]

// On some platforms, the alignment of primitives is less than their size.
#[repr(align(4))]
struct AlignedI32(i32);
#[repr(align(8))]
struct AlignedI64(i64);

const _: () = {
    let mut data = AlignedI32(42);
    let ptr = &mut data as *mut AlignedI32;
    assert!(ptr.is_aligned());

    // At runtime either `ptr1` or `ptr2` would be aligned, but at compiletime neither is aligned.
    let ptr1 = ptr.cast::<AlignedI64>();
    let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
    assert!(!ptr1.is_aligned());
    assert!(!ptr2.is_aligned());
};

Due to this behavior, it is possible that a runtime pointer derived from a compiletime pointer is aligned, even if the compiletime pointer wasn’t aligned.

#![feature(pointer_is_aligned)]
#![feature(const_pointer_is_aligned)]

// On some platforms, the alignment of primitives is less than their size.
#[repr(align(4))]
struct AlignedI32(i32);
#[repr(align(8))]
struct AlignedI64(i64);

// At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
// Also, note that mutable references are not allowed in the final value of constants.
const COMPTIME_PTR: *mut AlignedI32 = (&AlignedI32(42) as *const AlignedI32).cast_mut();
const _: () = assert!(!COMPTIME_PTR.cast::<AlignedI64>().is_aligned());
const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).cast::<AlignedI64>().is_aligned());

// At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
let runtime_ptr = COMPTIME_PTR;
assert_ne!(
    runtime_ptr.cast::<AlignedI64>().is_aligned(),
    runtime_ptr.wrapping_add(1).cast::<AlignedI64>().is_aligned(),
);

If a pointer is created from a fixed address, this function behaves the same during runtime and compiletime.

#![feature(pointer_is_aligned)]
#![feature(const_pointer_is_aligned)]

// On some platforms, the alignment of primitives is less than their size.
#[repr(align(4))]
struct AlignedI32(i32);
#[repr(align(8))]
struct AlignedI64(i64);

const _: () = {
    let ptr = 40 as *mut AlignedI32;
    assert!(ptr.is_aligned());

    // For pointers with a known address, runtime and compiletime behavior are identical.
    let ptr1 = ptr.cast::<AlignedI64>();
    let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
    assert!(ptr1.is_aligned());
    assert!(!ptr2.is_aligned());
};
const: unstable · source

pub fn is_aligned_to(self, align: usize) -> bool

🔬This is a nightly-only experimental API. (pointer_is_aligned)

Returns whether the pointer is aligned to align.

For non-Sized pointees this operation considers only the data pointer, ignoring the metadata.

Panics

The function panics if align is not a power-of-two (this includes 0).

Examples
#![feature(pointer_is_aligned)]
#![feature(pointer_byte_offsets)]

// On some platforms, the alignment of i32 is less than 4.
#[repr(align(4))]
struct AlignedI32(i32);

let mut data = AlignedI32(42);
let ptr = &mut data as *mut AlignedI32;

assert!(ptr.is_aligned_to(1));
assert!(ptr.is_aligned_to(2));
assert!(ptr.is_aligned_to(4));

assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));

assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
At compiletime

Note: Alignment at compiletime is experimental and subject to change. See the tracking issue for details.

At compiletime, the compiler may not know where a value will end up in memory. Calling this function on a pointer created from a reference at compiletime will only return true if the pointer is guaranteed to be aligned. This means that the pointer cannot be stricter aligned than the reference’s underlying allocation.

#![feature(pointer_is_aligned)]
#![feature(const_pointer_is_aligned)]
#![feature(const_mut_refs)]

// On some platforms, the alignment of i32 is less than 4.
#[repr(align(4))]
struct AlignedI32(i32);

const _: () = {
    let mut data = AlignedI32(42);
    let ptr = &mut data as *mut AlignedI32;

    assert!(ptr.is_aligned_to(1));
    assert!(ptr.is_aligned_to(2));
    assert!(ptr.is_aligned_to(4));

    // At compiletime, we know for sure that the pointer isn't aligned to 8.
    assert!(!ptr.is_aligned_to(8));
    assert!(!ptr.wrapping_add(1).is_aligned_to(8));
};

Due to this behavior, it is possible that a runtime pointer derived from a compiletime pointer is aligned, even if the compiletime pointer wasn’t aligned.

#![feature(pointer_is_aligned)]
#![feature(const_pointer_is_aligned)]

// On some platforms, the alignment of i32 is less than 4.
#[repr(align(4))]
struct AlignedI32(i32);

// At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
// Also, note that mutable references are not allowed in the final value of constants.
const COMPTIME_PTR: *mut AlignedI32 = (&AlignedI32(42) as *const AlignedI32).cast_mut();
const _: () = assert!(!COMPTIME_PTR.is_aligned_to(8));
const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).is_aligned_to(8));

// At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
let runtime_ptr = COMPTIME_PTR;
assert_ne!(
    runtime_ptr.is_aligned_to(8),
    runtime_ptr.wrapping_add(1).is_aligned_to(8),
);

If a pointer is created from a fixed address, this function behaves the same during runtime and compiletime.

#![feature(pointer_is_aligned)]
#![feature(const_pointer_is_aligned)]

const _: () = {
    let ptr = 40 as *mut u8;
    assert!(ptr.is_aligned_to(1));
    assert!(ptr.is_aligned_to(2));
    assert!(ptr.is_aligned_to(4));
    assert!(ptr.is_aligned_to(8));
    assert!(!ptr.is_aligned_to(16));
};

Trait Implementations§

1.0.0 · source§

impl<T> Clone for *mut Twhere T: ?Sized,

source§

fn clone(&self) -> *mut T

Returns a copy of the value. Read more
1.0.0 · source§

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
1.0.0 · source§

impl<T> Debug for *mut Twhere T: ?Sized,

source§

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
source§

impl Encode for *mut Object

source§

fn encode() -> Encoding

Returns the Objective-C type encoding for Self.
1.0.0 · source§

impl<T> Hash for *mut Twhere T: ?Sized,

source§

fn hash<H>(&self, state: &mut H)where H: Hasher,

Feeds this value into the given Hasher. Read more
1.3.0 · source§

fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
1.0.0 · source§

impl<T> Ord for *mut Twhere T: ?Sized,

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fn cmp(&self, other: &*mut T) -> Ordering

This method returns an Ordering between self and other. Read more
1.21.0 · source§

fn max(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · source§

fn min(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 · source§

fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval. Read more
1.0.0 · source§

impl<T> PartialEq<*mut T> for *mut Twhere T: ?Sized,

source§

fn eq(&self, other: &*mut T) -> bool

This method tests for self and other values to be equal, and is used by ==.
1.0.0 · source§

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · source§

impl<T> PartialOrd<*mut T> for *mut Twhere T: ?Sized,

source§

fn partial_cmp(&self, other: &*mut T) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &*mut T) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &*mut T) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &*mut T) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &*mut T) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
1.0.0 · source§

impl<T> Pointer for *mut Twhere T: ?Sized,

source§

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.
source§

impl<T> SimdElement for *mut Twhere T: Pointee<Metadata = ()>,

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type Mask = isize

🔬This is a nightly-only experimental API. (portable_simd)
The mask element type corresponding to this element type.
source§

impl<T, U> CoerceUnsized<*const U> for *mut Twhere T: Unsize<U> + ?Sized, U: ?Sized,

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impl<T, U> CoerceUnsized<*mut U> for *mut Twhere T: Unsize<U> + ?Sized, U: ?Sized,

1.0.0 · source§

impl<T> Copy for *mut Twhere T: ?Sized,

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impl<T, U> DispatchFromDyn<*mut U> for *mut Twhere T: Unsize<U> + ?Sized, U: ?Sized,

1.0.0 · source§

impl<T> Eq for *mut Twhere T: ?Sized,

1.0.0 · source§

impl<T> !Send for *mut Twhere T: ?Sized,

1.0.0 · source§

impl<T> !Sync for *mut Twhere T: ?Sized,

1.38.0 · source§

impl<T> Unpin for *mut Twhere T: ?Sized,

1.9.0 · source§

impl<T> UnwindSafe for *mut Twhere T: RefUnwindSafe + ?Sized,