sync: Implement From<T>
for OnceCell<T>
#3877
Merged
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Motivation
std::lazy::OnceCell
implementsFrom<T>
forOnceCell<T>
, buttokio::sync::OnceCell
does not. Generally, tokio tries to match std's API as closely as possible, so this could be considered an API hole.Solution
This PR adds that implementation. While this is a niche case, it also allows
tokio::OnceCell
to be constructed from aT
. As it is right now, one can construct an uninitializedOnceCell
withnew
andconst_new
, or one that may or may not be initialized usingnew_with
, but it is not possible to construct one directly from aT
(although this could be done withnew_with(Some(T))
).