add some comments to code snippets

[web.git] / ralf / _posts / 2018-04-05-a-formal-look-at-pinning.md

diff --git a/ralf/_posts/2018-04-05-a-formal-look-at-pinning.md b/ralf/_posts/2018-04-05-a-formal-look-at-pinning.md
index edaf6c64632381a5783fec2eec4dfb3a125660e6..5e51e7c747dbc01a0307a5f343b28e21cd27997c 100644 (file)
--- a/ralf/_posts/2018-04-05-a-formal-look-at-pinning.md
+++ b/ralf/_posts/2018-04-05-a-formal-look-at-pinning.md
@@ -34,7 +34,7 @@ The short version is that I view Rust types with private invariants as not havin
 You may be wondering why sharing is a separate typestate here; shouldn't that just be read-only access to a `T` that someone else owns?
 However, that clearly doesn't work for `&Cell`; to explain types with interior mutability we *need* sharing as a separate state.
 I explained this in more detail in the previous post, but as a quick example consider that, if you fully own a `RefCell`, the first field (storing the current count of readers/writers) has no special meaning whatsoever.
 You may be wondering why sharing is a separate typestate here; shouldn't that just be read-only access to a `T` that someone else owns?
 However, that clearly doesn't work for `&Cell`; to explain types with interior mutability we *need* sharing as a separate state.
 I explained this in more detail in the previous post, but as a quick example consider that, if you fully own a `RefCell`, the first field (storing the current count of readers/writers) has no special meaning whatsoever.

-This is witnessed by [`RefCell::get_mut`](https://doc.rust-lang.org/beta/std/cell/struct.RefCell.html#method.get_mut) ignoring that field.
+This is witnessed by [`RefCell::get_mut`](https://doc.rust-lang.org/stable/std/cell/struct.RefCell.html#method.get_mut) ignoring that field.

 In fact, it would be sound to add a `RefCell::reset(&mut self)` that just resets this field to `0`.
 
 ## Pinning
 In fact, it would be sound to add a `RefCell::reset(&mut self)` that just resets this field to `0`.
 
 ## Pinning


@@ -44,7 +44,7 @@ The core piece of the pinning API is a new reference type `Pin<'a, T>` that guar
 Crucially, **pinning does not provide immovable types**!
 Data is only pinned after a `Pin<T>` pointing to it has been created; it can be moved freely before that happens.
 
 Crucially, **pinning does not provide immovable types**!
 Data is only pinned after a `Pin<T>` pointing to it has been created; it can be moved freely before that happens.
 

-The [corresponding RFC](https://github.com/rust-lang/rfcs/blob/master/text/2349-pin.md) explains the entirey new API surface in quite some detail: [`Pin`](https://doc.rust-lang.org/nightly/std/mem/struct.Pin.html), [`PinBox`](https://doc.rust-lang.org/nightly/std/boxed/struct.PinBox.html) and the [`Unpin`](https://doc.rust-lang.org/nightly/std/marker/trait.Unpin.html) marker trait.
+The [corresponding RFC](https://github.com/rust-lang/rfcs/blob/master/text/2349-pin.md) explains the entirey new API surface in quite some detail: [`Pin`](https://doc.rust-lang.org/1.27.0/std/mem/struct.Pin.html), [`PinBox`](https://doc.rust-lang.org/1.27.0/std/boxed/struct.PinBox.html) and the [`Unpin`](https://doc.rust-lang.org/1.27.0/std/marker/trait.Unpin.html) marker trait.

 I will not repeat that here but only show one example of how to use `Pin` references and exploit their guarantees:
 {% highlight rust %}
 #![feature(pin, arbitrary_self_types, optin_builtin_traits)]
 I will not repeat that here but only show one example of how to use `Pin` references and exploit their guarantees:
 {% highlight rust %}
 #![feature(pin, arbitrary_self_types, optin_builtin_traits)]


@@ -68,11 +68,11 @@ impl SelfReferential {
     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.
     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 = &mut this.data as *const i32;
+        this.self_ref = &this.data as *const i32;

     }
 
     }
 

-    fn read_ref(mut self: Pin<SelfReferential>) -> Option<i32> {
-        let this : &mut SelfReferential = unsafe { Pin::get_mut(&mut self) };
+    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
         // Dereference self_ref if it is non-NULL.
         if this.self_ref == ptr::null() {
             None