"Benno Lossin" <lossin@xxxxxxxxxx> writes:
> On Thu Jul 3, 2025 at 11:03 AM CEST, Andreas Hindborg wrote:
>> "Benno Lossin" <lossin@xxxxxxxxxx> writes:
>>> On Wed Jul 2, 2025 at 3:18 PM CEST, Andreas Hindborg wrote:
[...]
>>>> + Some(unsafe { &*self.value.get() })
>>>> + } else {
>>>> + None
>>>> + }
>>>> + }
>>>> +
>>>> + /// Populate the [`OnceLock`].
>>>> + ///
>>>> + /// Returns `true` if the [`OnceLock`] was successfully populated.
>>>> + pub fn populate(&self, value: T) -> bool {
>>>> + // INVARIANT: We obtain exclusive access to the contained allocation and write 1 to
>>>> + // `init`.
>>>> + if let Ok(0) = self.init.cmpxchg(0, 1, Acquire) {
>>>> + // SAFETY: We obtained exclusive access to the contained object.
>>>> + unsafe { core::ptr::write(self.value.get(), value) };
>>>> + // INVARIANT: We release our exclusive access and transition the object to shared
>>>> + // access.
>>>> + self.init.store(2, Release);
>>>> + true
>>>> + } else {
>>>> + false
>>>> + }
>>>> + }
>>>> +}
>>>> +
>>>> +impl<T: Copy> OnceLock<T> {
>>>> + /// Get a copy of the contained object.
>>>> + ///
>>>> + /// Returns [`None`] if the [`OnceLock`] is empty.
>>>> + pub fn copy(&self) -> Option<T> {
>>>> + if self.init.load(Acquire) == 2 {
>>>> + // SAFETY: As determined by the load above, the object is ready for shared access.
>>>> + Some(unsafe { *self.value.get() })
>>>> + } else {
>>>> + None
>>>> + }
>>>
>>> The impl can just be:
>>>
>>> self.as_ref().copied()
>>
>> Nice. I was thinking of dropping this method and just have callers do
>>
>> my_once_lock.as_ref().map(|v| v.copied())
>>
>> What do you think?
>
> There is `Option::copied`, so no need for the `.map` call.
Cool.
> I don't
> really have a preference, if users always want to access it by-value,
> then we should have `copy`.
But should it be `copy` or `copied` like `Option`?
Best regards,
Andreas Hindborg
