Clarified exercise 11.1.

[rust-101.git] / src / part07.rs

diff --git a/src/part07.rs b/src/part07.rs
index 65449951eaf37a9fd17b188395296577545fa6a1..e395ba622af9cb3a1dc46f66940c79d26bc3be9b 100644 (file)
--- a/src/part07.rs
+++ b/src/part07.rs
@@ -4,8 +4,8 @@
 pub use part05::BigInt;
 
 // With our new knowledge of lifetimes, we are now able to write down the desired type of `min`:
 pub use part05::BigInt;
 
 // With our new knowledge of lifetimes, we are now able to write down the desired type of `min`:

-//@ We want the function to take two borrows *of the same lifetime*, and then
-//@ return a borrow of that lifetime. If the two input lifetimes would be different, we
+//@ We want the function to take two references *with the same lifetime*, and then
+//@ return a reference with that lifetime. If the two input lifetimes would be different, we

 //@ would not know which lifetime to use for the result.
 pub trait Minimum {
     fn min<'a>(&'a self, other: &'a Self) -> &'a Self;
 //@ would not know which lifetime to use for the result.
 pub trait Minimum {
     fn min<'a>(&'a self, other: &'a Self) -> &'a Self;


@@ -17,17 +17,17 @@ pub trait Minimum {
 pub fn vec_min<T: Minimum>(v: &Vec<T>) -> Option<&T> {
     let mut min: Option<&T> = None;
     for e in v {
 pub fn vec_min<T: Minimum>(v: &Vec<T>) -> Option<&T> {
     let mut min: Option<&T> = None;
     for e in v {

-        min = Some(match min {                                      /*@*/
-            None => e,                                              /*@*/
-            Some(n) => n.min(e)                                     /*@*/
-        });                                                         /*@*/
+        min = Some(match min {
+            None => e,
+            Some(n) => n.min(e)
+        });

     }
     min
 }
 //@ Notice that the return type `Option<&T>` is technically (leaving the borrowing story aside) a
 //@ pointer to a `T`, that could optionally be invalid. In other words, it's just like a pointer in
 //@ C(++) or Java that can be `NULL`! However, thanks to `Option` being an `enum`, we cannot forget
     }
     min
 }
 //@ Notice that the return type `Option<&T>` is technically (leaving the borrowing story aside) a
 //@ pointer to a `T`, that could optionally be invalid. In other words, it's just like a pointer in
 //@ C(++) or Java that can be `NULL`! However, thanks to `Option` being an `enum`, we cannot forget

-//@ to check the pointer for validity, avoiding the safety issues of C(++).<br/>
+//@ to check the pointer for validity, avoiding the safety issues of C(++). <br/>

 //@ Also, if you are worried about wasting space, notice that Rust knows that `&T` can never be
 //@ `NULL`, and hence optimizes `Option<&T>` to be no larger than `&T`. The `None` case is represented
 //@ as `NULL`. This is another great example of a zero-cost abstraction: `Option<&T>` is exactly like
 //@ Also, if you are worried about wasting space, notice that Rust knows that `&T` can never be
 //@ `NULL`, and hence optimizes `Option<&T>` to be no larger than `&T`. The `None` case is represented
 //@ as `NULL`. This is another great example of a zero-cost abstraction: `Option<&T>` is exactly like


@@ -35,7 +35,7 @@ pub fn vec_min<T: Minimum>(v: &Vec<T>) -> Option<&T> {
 
 // **Exercise 07.1**: For our `vec_min` to be usable with `BigInt`, you will have to provide an implementation of
 // `Minimum`. You should be able to pretty much copy the code you wrote for exercise 06.1. You should *not*
 
 // **Exercise 07.1**: For our `vec_min` to be usable with `BigInt`, you will have to provide an implementation of
 // `Minimum`. You should be able to pretty much copy the code you wrote for exercise 06.1. You should *not*

-// make any copies!
+// make any copies of `BigInt`!

 impl Minimum for BigInt {
     fn min<'a>(&'a self, other: &'a Self) -> &'a Self {
         unimplemented!()
 impl Minimum for BigInt {
     fn min<'a>(&'a self, other: &'a Self) -> &'a Self {
         unimplemented!()


@@ -62,16 +62,16 @@ impl PartialEq for BigInt {
 
 //@ Since implementing `PartialEq` is a fairly mechanical business, you can let Rust automate this
 //@ by adding the attribute `derive(PartialEq)` to the type definition. In case you wonder about
 
 //@ Since implementing `PartialEq` is a fairly mechanical business, you can let Rust automate this
 //@ by adding the attribute `derive(PartialEq)` to the type definition. In case you wonder about

-//@ the "partial", I suggest you check out the documentation of [`PartialEq`](http://doc.rust-lang.org/std/cmp/trait.PartialEq.html)
-//@ and [`Eq`](http://doc.rust-lang.org/std/cmp/trait.Eq.html). `Eq` can be automatically derived as well.
+//@ the "partial", I suggest you check out the documentation of [`PartialEq`](https://doc.rust-lang.org/std/cmp/trait.PartialEq.html)
+//@ and [`Eq`](https://doc.rust-lang.org/std/cmp/trait.Eq.html). `Eq` can be automatically derived as well.

 
 

-// Now we can compare `BigInt`s. Rust treats `PratialEq` special in that it is wired to the operator `==`:
-//@ That operator can not be used on our numbers! Speaking in C++ terms, we just overloaded the `==` operator
+// Now we can compare `BigInt`s. Rust treats `PartialEq` special in that it is wired to the operator `==`:
+//@ That operator can now be used on our numbers! Speaking in C++ terms, we just overloaded the `==` operator

 //@ for `BigInt`. Rust does not have function overloading (i.e., it will not dispatch to different
 //@ functions depending on the type of the argument). Instead, one typically finds (or defines) a
 //@ trait that catches the core characteristic common to all the overloads, and writes a single
 //@ function that's generic in the trait. For example, instead of overloading a function for all
 //@ for `BigInt`. Rust does not have function overloading (i.e., it will not dispatch to different
 //@ functions depending on the type of the argument). Instead, one typically finds (or defines) a
 //@ trait that catches the core characteristic common to all the overloads, and writes a single
 //@ function that's generic in the trait. For example, instead of overloading a function for all

-//@ the ways a string can be represented, one writes a generic functions over [ToString](http://doc.rust-lang.org/std/string/trait.ToString.html).
+//@ the ways a string can be represented, one writes a generic functions over [ToString](https://doc.rust-lang.org/std/string/trait.ToString.html).

 //@ Usually, there is a trait like this that fits the purpose - and if there is, this has the great
 //@ advantage that any type *you* write, that can convert to a string, just has to implement
 //@ that trait to be immediately usable with all the functions out there that generalize over `ToString`.
 //@ Usually, there is a trait like this that fits the purpose - and if there is, this has the great
 //@ advantage that any type *you* write, that can convert to a string, just has to implement
 //@ that trait to be immediately usable with all the functions out there that generalize over `ToString`.


@@ -113,7 +113,7 @@ fn test_min() {
 //@ that users can understand, while `Debug` is meant to show the internal state of data and targeted at
 //@ the programmer. The latter is what we want for `assert_eq!`, so let's get started.
 
 //@ that users can understand, while `Debug` is meant to show the internal state of data and targeted at
 //@ the programmer. The latter is what we want for `assert_eq!`, so let's get started.
 

-// All formating is handled by [`std::fmt`](http://doc.rust-lang.org/std/fmt/index.html). I won't explain
+// All formating is handled by [`std::fmt`](https://doc.rust-lang.org/std/fmt/index.html). I won't explain

 // all the details, and refer you to the documentation instead.
 use std::fmt;
 
 // all the details, and refer you to the documentation instead.
 use std::fmt;
 


@@ -147,4 +147,4 @@ fn test_vec_min() {
 // of course, need a `Display` bound on `T`.) Then you should be able to use them with `println!` just like you do
 // with numbers, and get rid of the inherent functions to print `SomethingOrNothing<i32>` and `SomethingOrNothing<f32>`.
 
 // of course, need a `Display` bound on `T`.) Then you should be able to use them with `println!` just like you do
 // with numbers, and get rid of the inherent functions to print `SomethingOrNothing<i32>` and `SomethingOrNothing<f32>`.
 

-//@ [index](main.html) | [previous](part06.html) | [next](main.html)
+//@ [index](main.html) | [previous](part06.html) | [raw source](workspace/src/part07.rs) | [next](part08.html)