Created
April 30, 2020 08:39
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#![feature(pin, arbitrary_self_types, optin_builtin_traits)] | |
use std::ptr; | |
use std::mem::Pin; | |
use std::boxed::PinBox; | |
use std::marker::Unpin; | |
struct SelfReferential { | |
data: i32, | |
self_ref: *const i32, | |
} | |
impl !Unpin for SelfReferential {} | |
impl SelfReferential { | |
fn new() -> SelfReferential { | |
SelfReferential { data: 42, self_ref: ptr::null() } | |
} | |
fn init(mut self: Pin<SelfReferential>) { | |
let this : &mut SelfReferential = unsafe { Pin::get_mut(&mut self) }; | |
// Set up self_ref to point to this.data. | |
this.self_ref = &this.data as *const i32; | |
} | |
fn read_ref(self: Pin<SelfReferential>) -> Option<i32> { | |
let this : &SelfReferential = &*self; | |
// Dereference self_ref if it is non-NULL. | |
if this.self_ref == ptr::null() { | |
None | |
} else { | |
Some(unsafe { *this.self_ref }) | |
} | |
} | |
} | |
fn main() { | |
let mut s = PinBox::new(SelfReferential::new()); | |
s.as_pin().init(); | |
println!("{:?}", s.as_pin().read_ref()); // prints Some(42) | |
} |
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