Better name for inc_print_even

[rust-101.git] / src / part05.rs

diff --git a/src/part05.rs b/src/part05.rs
index b593360122a7ba8beb277a494f2e3eb48c555056..eaad9804aaad71226c1bf3332839d32c73bbd9ce 100644 (file)
--- a/src/part05.rs
+++ b/src/part05.rs
@@ -48,8 +48,10 @@ impl BigInt {
     }
 
     // We can convert any vector of digits into a number, by removing trailing zeros. The `mut`
-    // declaration for `v` here is just like the one in `let mut ...`, it says that we will locally
-    // change the vector `v`.
+    // declaration for `v` here is just like the one in `let mut ...`: We completely own `v`, but Rust
+    // still asks us to make our intention of modifying it explicit. This `mut` is *not* part of the
+    // type of `from_vec` - the caller has to give up ownership of `v` anyway, so they don't care anymore
+    // what you do to it.
     // 
     // **Exercise 05.1**: Implement this function.
     // 
@@ -60,17 +62,17 @@ impl BigInt {
 }
 
 // ## Cloning
-//@ If you have a close look at the type of `BigInt::from_vec`, you will notice that it
-//@ consumes the vector `v`. The caller hence loses access to its vector. There is however something
+//@ If you take a close look at the type of `BigInt::from_vec`, you will notice that it
+//@ consumes the vector `v`. The caller hence loses access to its vector. However, there is something
 //@ we can do if we don't want that to happen: We can explicitly `clone` the vector,
 //@ which means that a full (or *deep*) copy will be performed. Technically,
-//@ `clone` takes a borrowed vector, and returns a fully owned one.
+//@ `clone` takes a borrowed vector in the form of a shared reference, and returns a fully owned one.
 fn clone_demo() {
     let v = vec![0,1 << 16];
     let b1 = BigInt::from_vec((&v).clone());
     let b2 = BigInt::from_vec(v);
 }
-//@ Rust has special treatment for methods that borrow its `self` argument (like `clone`, or
+//@ Rust has special treatment for methods that borrow their `self` argument (like `clone`, or
 //@ like `test_invariant` above): It is not necessary to explicitly borrow the receiver of the
 //@ method. Hence you could replace `(&v).clone()` by `v.clone()` above. Just try it!
 
@@ -97,7 +99,7 @@ impl<T: Clone> Clone for SomethingOrNothing<T> {
         match *self {                                               /*@*/
             Nothing => Nothing,                                     /*@*/
             //@ In the second arm of the match, we need to talk about the value `v`
-            //@ that's stored in `self`. However, if we would write the pattern as
+            //@ that's stored in `self`. However, if we were to write the pattern as
             //@ `Something(v)`, that would indicate that we *own* `v` in the code
             //@ after the arrow. That can't work though, we have to leave `v` owned by
             //@ whoever called us - after all, we don't even own `self`, we just borrowed it.
@@ -111,18 +113,18 @@ impl<T: Clone> Clone for SomethingOrNothing<T> {
 //@ `#[derive(Clone)]` right before the definition of `SomethingOrNothing`.
 
 // **Exercise 05.2**: Write some more functions on `BigInt`. What about a function that returns the number of
-// digits? The number of non-zero digits? The smallest/largest digit? Of course, these should all just borrow `self`.
+// digits? The number of non-zero digits? The smallest/largest digit? Of course, these should all take `self` as a shared reference (i.e., in borrowed form).
 
 // ## Mutation + aliasing considered harmful (part 2)
-//@ Now that we know how to borrow a part of an `enum` (like `v` above), there's another example for why we
+//@ Now that we know how to create references to contents of an `enum` (like `v` above), there's another example we can look at for why we
 //@ have to rule out mutation in the presence of aliasing. First, we define an `enum` that can hold either
 //@ a number, or a string.
 enum Variant {
     Number(i32),
     Text(String),
 }
-//@ Now consider the following piece of code. Like above, `n` will be a borrow of a part of `var`,
-//@ and since we wrote `ref mut`, the borrow will be mutable. In other words, right after the match, `ptr`
+//@ Now consider the following piece of code. Like above, `n` will be a reference to a part of `var`,
+//@ and since we wrote `ref mut`, the reference will be unique and mutable. In other words, right after the match, `ptr`
 //@ points to the number that's stored in `var`, where `var` is a `Number`. Remember that `_` means
 //@ "we don't care".
 fn work_on_variant(mut var: Variant, text: String) {
@@ -145,4 +147,4 @@ fn work_on_variant(mut var: Variant, text: String) {
 //@ I hope this example clarifies why Rust has to rule out mutation in the presence of aliasing *in general*,
 //@ not just for the specific case of a buffer being reallocated, and old pointers becoming hence invalid.
 
-//@ [index](main.html) | [previous](part04.html) | [next](part06.html)
+//@ [index](main.html) | [previous](part04.html) | [raw source](workspace/src/part05.rs) | [next](part06.html)