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Rollup merge of #85826 - jsha:npo, r=joshtriplett

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Mention "null pointer optimization" in option docs.

I had seen people discuss "null pointer optimization," but when I tried to find official documentation (using Google), the `std::option` page didn't show up, because it doesn't use that term. Hopefully adding the term will help others find it in the future.
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Guillaume Gomez 2021-06-01 11:29:44 +02:00 committed by GitHub
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library/core/src/option.rs
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@ -83,6 +83,8 @@
//! * [`ptr::NonNull<U>`]
//! * `#[repr(transparent)]` struct around one of the types in this list.
//!
//! This is called the "null pointer optimization" or NPO.
//!
//! It is further guaranteed that, for the cases above, one can
//! [`mem::transmute`] from all valid values of `T` to `Option<T>` and
//! from `Some::<T>(_)` to `T` (but transmuting `None::<T>` to `T`