Function core::ptr::eq

1.17.0 · source · []
pub fn eq<T: ?Sized>(a: *const T, b: *const T) -> bool
Expand description

Compares raw pointers for equality.

This is the same as using the == operator, but less generic: the arguments have to be *const T raw pointers, not anything that implements PartialEq.

This can be used to compare &T references (which coerce to *const T implicitly) by their address rather than comparing the values they point to (which is what the PartialEq for &T implementation does).


use std::ptr;

let five = 5;
let other_five = 5;
let five_ref = &five;
let same_five_ref = &five;
let other_five_ref = &other_five;

assert!(five_ref == same_five_ref);
assert!(ptr::eq(five_ref, same_five_ref));

assert!(five_ref == other_five_ref);
assert!(!ptr::eq(five_ref, other_five_ref));

Slices are also compared by their length (fat pointers):

let a = [1, 2, 3];
assert!(std::ptr::eq(&a[..3], &a[..3]));
assert!(!std::ptr::eq(&a[..2], &a[..3]));
assert!(!std::ptr::eq(&a[0..2], &a[1..3]));

Traits are also compared by their implementation:

struct Wrapper { member: i32 }

trait Trait {}
impl Trait for Wrapper {}
impl Trait for i32 {}

let wrapper = Wrapper { member: 10 };

// Pointers have equal addresses.
    &wrapper as *const Wrapper as *const u8,
    &wrapper.member as *const i32 as *const u8

// Objects have equal addresses, but `Trait` has different implementations.
    &wrapper as &dyn Trait,
    &wrapper.member as &dyn Trait,
    &wrapper as &dyn Trait as *const dyn Trait,
    &wrapper.member as &dyn Trait as *const dyn Trait,

// Converting the reference to a `*const u8` compares by address.
    &wrapper as &dyn Trait as *const dyn Trait as *const u8,
    &wrapper.member as &dyn Trait as *const dyn Trait as *const u8,