complete part 09

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

diff --git a/src/part05.rs b/src/part05.rs
index 3992fb1dcf7b6a7445bb6a0c0f1aee2846c4304c..b593360122a7ba8beb277a494f2e3eb48c555056 100644 (file)
--- a/src/part05.rs
+++ b/src/part05.rs
@@ -21,7 +21,7 @@
 //@ `data` public - otherwise, the next parts of this course could not work on `BigInt`s. Of course, in a
 //@ real program, one would make the field private to ensure that the invariant (no trailing zeros) is maintained.
 pub struct BigInt {
-    pub data: Vec<u64>,
+    pub data: Vec<u64>, // least significant digit first, no trailing zeros
 }
 
 // Now that we fixed the data representation, we can start implementing methods on it.
@@ -31,7 +31,7 @@ impl BigInt {
     //@ fields and initial values assigned to them.
     pub fn new(x: u64) -> Self {
         if x == 0 {
-            BigInt { data: vec![] }
+            BigInt { data: vec![] }                                 /*@*/
         } else {
             BigInt { data: vec![x] }                                /*@*/
         }
@@ -53,7 +53,7 @@ impl BigInt {
     // 
     // **Exercise 05.1**: Implement this function.
     // 
-    // *Hint*: You can use `pop()` to remove the last element of a vector.
+    // *Hint*: You can use `pop` to remove the last element of a vector.
     pub fn from_vec(mut v: Vec<u64>) -> Self {
         unimplemented!()
     }
@@ -111,7 +111,7 @@ 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?
+// digits? The number of non-zero digits? The smallest/largest digit? Of course, these should all just borrow `self`.
 
 // ## 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
@@ -131,7 +131,7 @@ fn work_on_variant(mut var: Variant, text: String) {
         Variant::Number(ref mut n) => ptr = n,
         Variant::Text(_) => return,
     }
-    /* var = Variant::Text(text); */
+    /* var = Variant::Text(text); */                                /* BAD! */
     *ptr = 1337;
 }
 //@ Now, imagine what would happen if we were permitted to also mutate `var`. We could, for example,