Add exercise 10.2 (#24)

[rust-101.git] / src / part00.rs

diff --git a/src/part00.rs b/src/part00.rs
index ed76e81f83469ffd80471ddf63fad053f1d57c1a..d8b4ed7bef7786efa986eff6e0afef421e7cf163 100644 (file)
--- a/src/part00.rs
+++ b/src/part00.rs
@@ -6,10 +6,10 @@
 
 //@ ## Getting started
 //@ Let us start by thinking about the *type* of our function. Rust forces us to give the types of
 
 //@ ## Getting started
 //@ Let us start by thinking about the *type* of our function. Rust forces us to give the types of

-//@ all arguments, and the return type, before we even start writing the body. In the case of our minimum
-//@ function, we may be inclined to say that it returns a number. But then we would be in trouble: What's
-//@ the minimum of an empty list? The type of the function says we have to return *something*.
-//@ We could just choose 0, but that would be kind of arbitrary. What we need
+//@ all arguments, and the return type, before we even start writing the body. In the case of our
+//@ minimum function, we may be inclined to say that it returns a number. But then we would be in
+//@ trouble: What's the minimum of an empty list? The type of the function says we have to return
+//@ *something*. We could just choose 0, but that would be kind of arbitrary. What we need

 //@ is a type that is "a number, or nothing". Such a type (of multiple exclusive options)
 //@ is called an "algebraic datatype", and Rust lets us define such types with the keyword `enum`.
 //@ Coming from C(++), you can think of such a type as a `union`, together with a field that
 //@ is a type that is "a number, or nothing". Such a type (of multiple exclusive options)
 //@ is called an "algebraic datatype", and Rust lets us define such types with the keyword `enum`.
 //@ Coming from C(++), you can think of such a type as a `union`, together with a field that


@@ -35,23 +35,26 @@ fn vec_min(vec: Vec<i32>) -> NumberOrNothing {
     //@ immutable per default, and you need to tell Rust if you want
     //@ to change a variable later.
 
     //@ immutable per default, and you need to tell Rust if you want
     //@ to change a variable later.
 

-    // Now we want to *iterate* over the list. Rust has some nice syntax for
-    // iterators:
+    // Now we want to *iterate* over the list. Rust has some nice syntax for iterators:

     for el in vec {
     for el in vec {

-        // So `el` is al element of the list. We need to update `min` accordingly, but how do we get the current
-        // number in there? This is what pattern matching can do:
+        // So `el` is an element of the list. We need to update `min` accordingly, but how do we
+        // get the current number in there? This is what pattern matching can do:

         match min {
         match min {

-            // In this case (*arm*) of the `match`, `min` is currently nothing, so let's just make it the number `el`.
+            // In this case (*arm*) of the `match`, `min` is currently nothing, so let's just make
+            // it the number `el`.

             NumberOrNothing::Nothing => {
                 min = NumberOrNothing::Number(el);                  /*@*/
             },
             NumberOrNothing::Nothing => {
                 min = NumberOrNothing::Number(el);                  /*@*/
             },

-            // In this arm, `min` is currently the number `n`, so let's compute the new minimum and store it.
+            // In this arm, `min` is currently the number `n`, so let's compute the new minimum and
+            // store it.

             //@ We will write the function `min_i32` just after we completed this one.
             NumberOrNothing::Number(n) => {
                 let new_min = min_i32(n, el);                       /*@*/
                 min = NumberOrNothing::Number(new_min);             /*@*/
             }
         }
             //@ We will write the function `min_i32` just after we completed this one.
             NumberOrNothing::Number(n) => {
                 let new_min = min_i32(n, el);                       /*@*/
                 min = NumberOrNothing::Number(new_min);             /*@*/
             }
         }

+        //@ Notice that Rust makes sure you did not forget to handle any case in your `match`. We
+        //@ say that the pattern matching has to be *exhaustive*.

     }
     // Finally, we return the result of the computation.
     return min;
     }
     // Finally, we return the result of the computation.
     return min;


@@ -71,22 +74,21 @@ fn min_i32(a: i32, b: i32) -> i32 {
 
 // Indeed, we can: The following line tells Rust to take
 // the constructors of `NumberOrNothing` into the local namespace.
 
 // Indeed, we can: The following line tells Rust to take
 // the constructors of `NumberOrNothing` into the local namespace.

-// Try moving that above the function, and removing all the occurrences `NumberOrNothing::`.
+// Try moving that above the function, and removing all the occurrences of `NumberOrNothing::`.

 use self::NumberOrNothing::{Number,Nothing};
 
 // To call this function, we now just need a list. Of course, ultimately we want to ask the user for
 // a list of numbers, but for now, let's just hard-code something.
 
 use self::NumberOrNothing::{Number,Nothing};
 
 // To call this function, we now just need a list. Of course, ultimately we want to ask the user for
 // a list of numbers, but for now, let's just hard-code something.
 

-//@ `vec!` is a *macro* (as you can tell from the `!`) that constructs a constant `Vec<_>` with the given
+//@ `vec!` is a *macro* (as indicated by `!`) that constructs a constant `Vec<_>` with the given

 //@ elements.
 fn read_vec() -> Vec<i32> {
     vec![18,5,7,1,9,27]                                             /*@*/
 }
 
 //@ elements.
 fn read_vec() -> Vec<i32> {
     vec![18,5,7,1,9,27]                                             /*@*/
 }
 

-// Finally, let's call our functions and run the code!
-// But, wait, we would like to actually see something, so we need to print the result.
-// Of course Rust can print numbers, but after calling `vec_min`, we have a `NumberOrNothing`.
-// So let's write a small helper function that prints such values.
+// Of course, we would also like to actually see the result of the computation, so we need to print the result.
+//@ Of course Rust can print numbers, but after calling `vec_min`, we have a `NumberOrNothing`.
+//@ So let's write a small helper function that prints such values.

 
 //@ `println!` is again a macro, where the first argument is a *format string*. For
 //@ now, you just need to know that `{}` is the placeholder for a value, and that Rust
 
 //@ `println!` is again a macro, where the first argument is a *format string*. For
 //@ now, you just need to know that `{}` is the placeholder for a value, and that Rust


@@ -105,11 +107,12 @@ pub fn main() {
     print_number_or_nothing(min);
 }
 
     print_number_or_nothing(min);
 }
 

-// You can now use `cargo build` to compile your code. If all goes well, try `cargo run` on the
-// console to run it.
+//@ You can now use `cargo build` to compile your *crate*. That's Rust's name for a *compilation unit*, which in
+//@ the case of Rust means an application or a library. <br/>
+// Finally, try `cargo run` on the console to run it.

 
 //@ Yay, it said "1"! That's actually the right answer. Okay, we could have
 
 //@ Yay, it said "1"! That's actually the right answer. Okay, we could have

-//@ computed that ourselves, but that's besides the point. More importantly:
+//@ computed that ourselves, but that's beside the point. More importantly:

 //@ You completed the first part of the course.
 
 //@ You completed the first part of the course.
 

-//@ [index](main.html) | previous | [next](part01.html)
+//@ [index](main.html) | previous | [raw source](workspace/src/part00.rs) | [next](part01.html)