minor edits

This commit is contained in:
Ralf Jung 2019-06-16 00:05:17 +02:00
parent c489636ce1
commit 665aa3e5bb

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@ -196,8 +196,8 @@
//! type should that reference have? Is it `Pin<&mut Field>` or `&mut Field`?
//! The same question arises with the fields of an enum, and also when considering
//! container/wrapper types such as [`Vec<T>`], [`Box<T>`], or [`RefCell<T>`].
//! Also, this question arises for both mutable and shared references, we just
//! use the more common case of mutable references here for illustration.
//! (This question applies to both mutable and shared references, we just
//! use the more common case of mutable references here for illustration.)
//!
//! It turns out that it is actually up to the author of the data structure
//! to decide whether the pinned projection for a particular field turns
@ -214,22 +214,22 @@
//!
//! ## Pinning *is not* structural for `field`
//!
//! It may seem counter-intuitive that the field of a pinned struct is not pinned,
//! It may seem counter-intuitive that the field of a pinned struct might not be pinned,
//! but that is actually the easiest choice: if a `Pin<&mut Field>` is never created,
//! nothing can go wrong! So, if you decide that some field does not have structural pinning,
//! all you have to ensure is that you never create a pinned reference to that field.
//!
//! Then you may add a projection method that turns `Pin<&mut Struct>` into `Pin<&mut Field>`:
//! Then you may add a projection method that turns `Pin<&mut Struct>` into `&mut Field`:
//! ```rust,ignore
//! impl Struct {
//! fn get_field<'a>(self: Pin<&'a mut Self>) -> &'a mut Field {
//! fn pin_get_field<'a>(self: Pin<&'a mut Self>) -> &'a mut Field {
//! // This is okay because `field` is never considered pinned.
//! unsafe { &mut self.get_unchecked_mut().field }
//! }
//! }
//! ```
//!
//! You may also make make `Struct: Unpin` *even if* the type of `field`
//! You may also `impl Unpin for Struct` *even if* the type of `field`
//! is not `Unpin`. What that type thinks about pinning is just not relevant
//! when no `Pin<&mut Field>` is ever created.
//!
@ -242,7 +242,7 @@
//! witnessing that the field is pinned:
//! ```rust,ignore
//! impl Struct {
//! fn get_field<'a>(self: Pin<&'a mut Self>) -> Pin<&'a mut Field> {
//! fn pin_get_field<'a>(self: Pin<&'a mut Self>) -> Pin<&'a mut Field> {
//! // This is okay because `field` is pinned when `self` is.
//! unsafe { self.map_unchecked_mut(|s| &mut s.field) }
//! }
@ -252,8 +252,8 @@
//! However, structural pinning comes with a few extra requirements:
//!
//! 1. The struct must only be [`Unpin`] if all the structural fields are
//! `Unpin`. This is the default, but `Unpin` is a safe trait, so it is your
//! responsibility as the author of the struct *not* to add something like
//! `Unpin`. This is the default, but `Unpin` is a safe trait, so as the author of
//! the struct it is your responsibility *not* to add something like
//! `impl<T> Unpin for Struct<T>`. (Notice that adding a projection operation
//! requires unsafe code, so the fact that `Unpin` is a safe trait does not break
//! the principle that you only have to worry about any of this if you use `unsafe`.)