Struct Alignment Copy item path

Returns the alignment for a type.

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

Returns the ABI-required minimum alignment of the type of the value that val points to.

Every reference to a value of the type T must be a multiple of this number.

§Examples

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

assert_eq!(Alignment::of_val(&5i32).as_usize(), 4);

Returns the ABI-required minimum alignment of the type of the value that val points to.

Every reference to a value of the type T must be a multiple of this number.

§Safety

This function is only safe to call if the following conditions hold:

• If T is Sized, this function is always safe to call.
• If the unsized tail of T is:
  • a slice, then the length of the slice tail must be an initialized integer, and the size of the entire value (dynamic tail length + statically sized prefix) must fit in isize. For the special case where the dynamic tail length is 0, this function is safe to call.
  • a trait object, then the vtable part of the pointer must point to a valid vtable acquired by an unsizing coercion, and the size of the entire value (dynamic tail length + statically sized prefix) must fit in isize.
  • an (unstable) extern type, then this function is always safe to call, but may panic or otherwise return the wrong value, as the extern type’s layout is not known. This is the same behavior as Alignment::of_val on a reference to a type with an extern type tail.
  • otherwise, it is conservatively not allowed to call this function.

§Examples

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

assert_eq!(unsafe { Alignment::of_val_raw(&5i32) }.as_usize(), 4);

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.

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.

Returns the alignment as a usize.

Returns the alignment as a NonZero<usize>.

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);

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);

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.