Added exemplary unit test for iter_mut().

[rust-101.git] / src / part16.rs

diff --git a/src/part16.rs b/src/part16.rs
index f5735b874e854eebcb4606721bc1c4c55cbce220..f0707aac6466e15ce1696e3bbd6e7c8c041efe47 100644 (file)
--- a/src/part16.rs
+++ b/src/part16.rs
@@ -32,7 +32,7 @@ struct Node<T> {
     data: T,
 }
 // A node pointer is a *mutable raw pointer* to a node.
     data: T,
 }
 // A node pointer is a *mutable raw pointer* to a node.

-//@ Raw pointers (`*mut T` and `*const T`) are the Rust equivalent of pointers in C. Unlike borrows, they do not come with
+//@ Raw pointers (`*mut T` and `*const T`) are the Rust equivalent of pointers in C. Unlike references, they do not come with

 //@ any guarantees: Raw pointers can be null, or they can point to garbage. They don't have a lifetime, either.
 type NodePtr<T> = *mut Node<T>;
 
 //@ any guarantees: Raw pointers can be null, or they can point to garbage. They don't have a lifetime, either.
 type NodePtr<T> = *mut Node<T>;
 


@@ -55,12 +55,12 @@ pub struct LinkedList<T> {
 //@ Clearly, that's an unsafe operation and must only be used with great care - or even better, not at all. Seriously.
 //@ If at all possible, you should never use `transmute`. <br/>
 //@ We are making the assumption here that a `Box` and a raw pointer have the same representation in memory. In the future,
 //@ Clearly, that's an unsafe operation and must only be used with great care - or even better, not at all. Seriously.
 //@ If at all possible, you should never use `transmute`. <br/>
 //@ We are making the assumption here that a `Box` and a raw pointer have the same representation in memory. In the future,

-//@ Rust will [provide](http://doc.rust-lang.org/beta/alloc/boxed/struct.Box.html#method.from_raw) such [operations](http://doc.rust-lang.org/beta/alloc/boxed/struct.Box.html#method.into_raw) in the standard library, but the exact API is still being fleshed out.
+//@ Rust will [provide](https://doc.rust-lang.org/beta/alloc/boxed/struct.Box.html#method.from_raw) such [operations](https://doc.rust-lang.org/beta/alloc/boxed/struct.Box.html#method.into_raw) in the standard library, but the exact API is still being fleshed out.

 
 //@ We declare `raw_into_box` to be an `unsafe` function, telling Rust that calling this function is not generally safe.
 //@ This grants us the unsafe powers for the body of the function: We can dereference raw pointers, and - most importantly - we
 
 //@ We declare `raw_into_box` to be an `unsafe` function, telling Rust that calling this function is not generally safe.
 //@ This grants us the unsafe powers for the body of the function: We can dereference raw pointers, and - most importantly - we

-//@ can call unsafe functions. (There's a third power, related to mutable static variables, but we didn't talk about static variables
-//@ in the course, so that won't be relevant here.) <br/>
+//@ can call unsafe functions. (The other unsafe powers won't be relevant here. Go read [The Rustonomicon](https://doc.rust-lang.org/nightly/nomicon/)
+//@ if you want to learn all about this, but be warned - That Way Lies Madness.) <br/>

 //@ Here, the caller will have to ensure that `r` is a valid pointer, and that nobody else has a pointer to this data.
 unsafe fn raw_into_box<T>(r: *mut T) -> Box<T> {
     mem::transmute(r)
 //@ Here, the caller will have to ensure that `r` is a valid pointer, and that nobody else has a pointer to this data.
 unsafe fn raw_into_box<T>(r: *mut T) -> Box<T> {
     mem::transmute(r)


@@ -84,7 +84,7 @@ impl<T> LinkedList<T> {
         //@ Calling `box_into_raw` gives up ownership of the box, which is crucial: We don't want the memory that it points to to be deallocated!
         let new = Box::new( Node { data: t, next: ptr::null_mut(), prev: self.last } );
         let new = box_into_raw(new);
         //@ Calling `box_into_raw` gives up ownership of the box, which is crucial: We don't want the memory that it points to to be deallocated!
         let new = Box::new( Node { data: t, next: ptr::null_mut(), prev: self.last } );
         let new = box_into_raw(new);

-        // Update other points to this node.
+        // Update other pointers to this node.

         if self.last.is_null() {
             debug_assert!(self.first.is_null());
             // The list is currently empty, so we have to update the head pointer.
         if self.last.is_null() {
             debug_assert!(self.first.is_null());
             // The list is currently empty, so we have to update the head pointer.


@@ -106,7 +106,7 @@ impl<T> LinkedList<T> {
 
     // Next, we are going to provide an iterator.
     //@ This function just creates an instance of `IterMut`, the iterator type which does the actual work.
 
     // Next, we are going to provide an iterator.
     //@ This function just creates an instance of `IterMut`, the iterator type which does the actual work.

-    pub fn iter_mut(&self) -> IterMut<T> {
+    pub fn iter_mut(&mut self) -> IterMut<T> {

         IterMut { next: self.first, _marker: PhantomData  }
     }
 }
         IterMut { next: self.first, _marker: PhantomData  }
     }
 }


@@ -115,7 +115,7 @@ impl<T> LinkedList<T> {
 //@ that it is going to visit. However, how do we make sure that this pointer remains valid? We have to
 //@ get this right ourselves, as we left the safe realms of borrowing and ownership. Remember that the
 //@ key ingredient for iterator safety was to tie the lifetime of the iterator to the lifetime of the
 //@ that it is going to visit. However, how do we make sure that this pointer remains valid? We have to
 //@ get this right ourselves, as we left the safe realms of borrowing and ownership. Remember that the
 //@ key ingredient for iterator safety was to tie the lifetime of the iterator to the lifetime of the

-//@ borrow used for `iter_mut`. We will thus give `IterMut` two parameters: A type parameter specifying
+//@ reference used for `iter_mut`. We will thus give `IterMut` two parameters: A type parameter specifying

 //@ the type of the data, and a lifetime parameter specifying for how long the list was borrowed to the
 //@ iterator.
 
 //@ the type of the data, and a lifetime parameter specifying for how long the list was borrowed to the
 //@ iterator.
 


@@ -123,7 +123,7 @@ impl<T> LinkedList<T> {
 //@ the data in the list lives at least as long as the iterator: If you drop the `T: 'a`, Rust will tell
 //@ you to add it back. And secondly, Rust will complain if `'a` is not actually used in the struct.
 //@ It doesn't know what it is supposed to do with that lifetime. So we use `PhantomData` again to tell
 //@ the data in the list lives at least as long as the iterator: If you drop the `T: 'a`, Rust will tell
 //@ you to add it back. And secondly, Rust will complain if `'a` is not actually used in the struct.
 //@ It doesn't know what it is supposed to do with that lifetime. So we use `PhantomData` again to tell

-//@ it that in terms of ownership, this type actually (mutably) borrows a linked list. This has no
+//@ it that in terms of ownership, this type actually (uniquely) borrows a linked list. This has no

 //@ operational effect, but it means that Rust can deduce the intent we had when adding that
 //@ seemingly useless lifetime parameter.
 pub struct IterMut<'a, T> where T: 'a {
 //@ operational effect, but it means that Rust can deduce the intent we had when adding that
 //@ seemingly useless lifetime parameter.
 pub struct IterMut<'a, T> where T: 'a {


@@ -141,7 +141,7 @@ impl<'a, T> Iterator for IterMut<'a, T> {
         if self.next.is_null() {
             None
         } else {
         if self.next.is_null() {
             None
         } else {

-            // Otherwise, we can convert the next pointer to a borrow, get a borrow to the data
+            // Otherwise, we can convert the next pointer to a reference, get a reference to the data

             // and update the iterator.
             let next = unsafe { &mut *self.next };
             let ret = &mut next.data;
             // and update the iterator.
             let next = unsafe { &mut *self.next };
             let ret = &mut next.data;


@@ -154,12 +154,12 @@ impl<'a, T> Iterator for IterMut<'a, T> {
 //@ In `next` above, we made crucial use of the assumption that `self.next` is either null or a valid pointer.
 //@ This only works because if someone tries to delete elements from a list during iteration, we know that the borrow checker
 //@ will catch them: If they call `next`, the lifetime `'a` we artificially added to the iterator has to still be
 //@ In `next` above, we made crucial use of the assumption that `self.next` is either null or a valid pointer.
 //@ This only works because if someone tries to delete elements from a list during iteration, we know that the borrow checker
 //@ will catch them: If they call `next`, the lifetime `'a` we artificially added to the iterator has to still be

-//@ active, which means the mutable borrow passed to `iter_mut` is still active, which means nobody can delete
+//@ active, which means the mutable reference passed to `iter_mut` is still active, which means nobody can delete

 //@ anything from the list. In other words, we make use of the expressive type system of Rust, decorating
 //@ our own unsafe implementation with just enough information so that Rust can check *uses* of the linked-list.
 //@ If the type system were weaker, we could not write a linked-list like the above with a safe interface!
 
 //@ anything from the list. In other words, we make use of the expressive type system of Rust, decorating
 //@ our own unsafe implementation with just enough information so that Rust can check *uses* of the linked-list.
 //@ If the type system were weaker, we could not write a linked-list like the above with a safe interface!
 

-// **Exercise 16.2**: Add a method `iter` and a type `Iter` providing iteration for shared borrows.
+// **Exercise 16.2**: Add a method `iter` and a type `Iter` providing iteration for shared references.

 // Add testcases for both kinds of iterators.
 
 // ## `Drop`
 // Add testcases for both kinds of iterators.
 
 // ## `Drop`


@@ -173,7 +173,7 @@ impl<'a, T> Iterator for IterMut<'a, T> {
 //@ of `LinkedList`.
 impl<T> Drop for LinkedList<T> {
     // The destructor itself is a method which takes `self` in mutably borrowed form. It cannot own `self`, because then
 //@ of `LinkedList`.
 impl<T> Drop for LinkedList<T> {
     // The destructor itself is a method which takes `self` in mutably borrowed form. It cannot own `self`, because then

-    // the destructor of `self` would be called at the end pf the function, resulting in endless recursion...
+    // the destructor of `self` would be called at the end of the function, resulting in endless recursion.

     fn drop(&mut self) {
         let mut cur_ptr = self.first;
         while !cur_ptr.is_null() {
     fn drop(&mut self) {
         let mut cur_ptr = self.first;
         while !cur_ptr.is_null() {


@@ -197,4 +197,4 @@ impl<T> Drop for LinkedList<T> {
 //@ extensions here and there. The [index](main.html) contains some more links to additional resources you may find useful. 
 //@ With that, there's only one thing left to say: Happy Rust Hacking!
 
 //@ extensions here and there. The [index](main.html) contains some more links to additional resources you may find useful. 
 //@ With that, there's only one thing left to say: Happy Rust Hacking!
 

-//@ [index](main.html) | [previous](part15.html) | next
+//@ [index](main.html) | [previous](part15.html) | [raw source](workspace/src/part16.rs) | next