Struct std::ptr::Alignment

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pub struct Alignment(/* private fields */);

🔬This is a nightly-only experimental API. (ptr_alignment_type #102070)

Expand description

A type storing a usize which is a power of two, and thus represents a possible alignment in the Rust abstract machine.

Note that particularly large alignments, while representable in this type, are likely not to be supported by actual allocators and linkers.

Implementations§

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impl Alignment

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pub const MIN: Alignment = _

🔬This is a nightly-only experimental API. (ptr_alignment_type #102070)

The smallest possible alignment, 1.

All addresses are always aligned at least this much.

§Examples

#![feature(ptr_alignment_type)]
use std::ptr::Alignment;

assert_eq!(Alignment::MIN.as_usize(), 1);

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pub const fn of<T>() -> Alignment

🔬This is a nightly-only experimental API. (ptr_alignment_type #102070)

Returns the alignment for a type.

This provides the same numerical value as mem::align_of, but in an Alignment instead of a usize.

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pub const fn new(align: usize) -> Option<Alignment>

🔬This is a nightly-only experimental API. (ptr_alignment_type #102070)

Creates an Alignment from a usize, or returns None if it’s not a power of two.

Note that 0 is not a power of two, nor a valid alignment.

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pub const unsafe fn new_unchecked(align: usize) -> Alignment

🔬This is a nightly-only experimental API. (ptr_alignment_type #102070)

Creates an Alignment from a power-of-two usize.

§Safety

align must be a power of two.

Equivalently, it must be 1 << exp for some exp in 0..usize::BITS. It must not be zero.

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pub const fn as_usize(self) -> usize

🔬This is a nightly-only experimental API. (ptr_alignment_type #102070)

Returns the alignment as a usize.

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pub const fn as_nonzero(self) -> NonZero<usize>

🔬This is a nightly-only experimental API. (ptr_alignment_type #102070)

Returns the alignment as a NonZero<usize>.

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pub const fn log2(self) -> u32

🔬This is a nightly-only experimental API. (ptr_alignment_type #102070)

Returns the base-2 logarithm of the alignment.

This is always exact, as self represents a power of two.

§Examples

#![feature(ptr_alignment_type)]
use std::ptr::Alignment;

assert_eq!(Alignment::of::<u8>().log2(), 0);
assert_eq!(Alignment::new(1024).unwrap().log2(), 10);

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pub const fn mask(self) -> usize

🔬This is a nightly-only experimental API. (ptr_alignment_type #102070)

Returns a bit mask that can be used to match this alignment.

This is equivalent to !(self.as_usize() - 1).

§Examples

#![feature(ptr_alignment_type)]
#![feature(ptr_mask)]
use std::ptr::{Alignment, NonNull};

#[repr(align(1))] struct Align1(u8);
#[repr(align(2))] struct Align2(u16);
#[repr(align(4))] struct Align4(u32);
let one = <NonNull<Align1>>::dangling().as_ptr();
let two = <NonNull<Align2>>::dangling().as_ptr();
let four = <NonNull<Align4>>::dangling().as_ptr();

assert_eq!(four.mask(Alignment::of::<Align1>().mask()), four);
assert_eq!(four.mask(Alignment::of::<Align2>().mask()), four);
assert_eq!(four.mask(Alignment::of::<Align4>().mask()), four);
assert_ne!(one.mask(Alignment::of::<Align4>().mask()), one);