Struct serde::lib::ptr::Alignment

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#[repr(transparent)]
pub struct Alignment(AlignmentEnum);

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

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.

Tuple Fields§

§0: AlignmentEnum

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

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)

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)

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)

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)

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)

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)

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)

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)

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);