This is no longer work-in-progress

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

diff --git a/src/part00.rs b/src/part00.rs
index c92200770debf3414acdc778a23ac88a8e3655af..6469907e91203f62f856a8a8e25c229c9b7a41c1 100644 (file)
--- a/src/part00.rs
+++ b/src/part00.rs
@@ -4,53 +4,51 @@
 // As our first piece of Rust code, we want to write a function that computes the
 // minimum of a list.
 
 // As our first piece of Rust code, we want to write a function that computes the
 // minimum of a list.
 

-// We are going to make use of the standard library, so let's import that:
-use std;
-
-// 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
-// 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
-// stores the variant of the union that's currently used.
+//@ ## 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
+//@ 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
+//@ stores the variant of the union that's currently used.

 
 // An `enum` for "a number or nothing" could look as follows:
 enum NumberOrNothing {
     Number(i32),
     Nothing
 }
 
 // An `enum` for "a number or nothing" could look as follows:
 enum NumberOrNothing {
     Number(i32),
     Nothing
 }

-// Notice that `i32` is the type of (signed, 32-bit) integers. To write down the type of
-// the minimum function, we need just one more ingredient: `Vec<i32>` is the type of
-// (growable) arrays of numbers, and we will use that as our list type.
+//@ Notice that `i32` is the type of (signed, 32-bit) integers. To write down the type of
+//@ the minimum function, we need just one more ingredient: `Vec<i32>` is the type of
+//@ (growable) arrays of numbers, and we will use that as our list type.

 
 // Observe how in Rust, the return type comes *after* the arguments.
 fn vec_min(vec: Vec<i32>) -> NumberOrNothing {
 
 // Observe how in Rust, the return type comes *after* the arguments.
 fn vec_min(vec: Vec<i32>) -> NumberOrNothing {

-    // In the function, we first need some variable to store the minimum as computed so far.
-    // Since we start out with nothing computed, this will again be a 
-    // "number or nothing":
+    //@ In the function, we first need some variable to store the minimum as computed so far.
+    //@ Since we start out with nothing computed, this will again be a 
+    //@ "number or nothing":

     let mut min = NumberOrNothing::Nothing;
     let mut min = NumberOrNothing::Nothing;

-    // We do not have to write a type next to `min`, Rust can figure that out automatically
-    // (a bit like `auto` in C++11). Also notice the `mut`: In Rust, variables are
-    // immutable per default, and you need to tell Rust if you want
-    // to change a variable later.
+    //@ We do not have to write a type next to `min`, Rust can figure that out automatically
+    //@ (a bit like `auto` in C++11). Also notice the `mut`: In Rust, variables are
+    //@ 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 {
         // 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:
         match min {
             // In this case (*arm*) of the `match`, `min` is currently nothing, so let's just make it the number `el`.
             NumberOrNothing::Nothing => {
     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:
         match min {
             // 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);
+                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) => {
             NumberOrNothing::Number(n) => {

-                let new_min = std::cmp::min(n, el);
-                min = NumberOrNothing::Number(new_min);
+                let new_min = min_i32(n, el);                       /*@*/
+                min = NumberOrNothing::Number(new_min);             /*@*/

             }
         }
     }
             }
         }
     }


@@ -58,6 +56,15 @@ fn vec_min(vec: Vec<i32>) -> NumberOrNothing {
     return min;
 }
 
     return min;
 }
 

+// Now that we reduced the problem to computing the minimum of two integers, let's do that.
+fn min_i32(a: i32, b: i32) -> i32 {
+    if a < b {
+        return a;                                                   /*@*/
+    } else {
+        return b;                                                   /*@*/
+    }
+}
+

 // Phew. We wrote our first Rust function! But all this `NumberOrNothing::` is getting kind of
 // ugly. Can't we do that nicer?
 
 // Phew. We wrote our first Rust function! But all this `NumberOrNothing::` is getting kind of
 // ugly. Can't we do that nicer?
 


@@ -69,25 +76,24 @@ 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.
 
 // 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
-// elements.
+//@ `vec!` is a *macro* (as you can tell from the `!`) that constructs a constant `Vec<_>` with the given
+//@ elements.

 fn read_vec() -> Vec<i32> {
 fn read_vec() -> Vec<i32> {

-    vec![18,5,7,1,9,27]
+    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
-// will check at compile-time that you supplied the right number of arguments.
+//@ `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
+//@ will check at compile-time that you supplied the right number of arguments.

 fn print_number_or_nothing(n: NumberOrNothing) {
 fn print_number_or_nothing(n: NumberOrNothing) {

-    match n {
-        Nothing => println!("The number is: <nothing>"),
-        Number(n) => println!("The number is: {}", n),
-    };
+    match n {                                                       /*@*/
+        Nothing => println!("The number is: <nothing>"),            /*@*/
+        Number(n) => println!("The number is: {}", n),              /*@*/
+    };                                                              /*@*/

 }
 
 // Putting it all together:
 }
 
 // Putting it all together:


@@ -97,10 +103,12 @@ pub fn main() {
     print_number_or_nothing(min);
 }
 
     print_number_or_nothing(min);
 }
 

-// Now try `cargo run` on the console to run above code.
+//@ 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
-// computed that ourselves, but that's besides the point. More importantly:
-// You completed the first part of the course.
+//@ 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:
+//@ You completed the first part of the course.

 
 

-// [index](main.html) | previous | [next](part01.html)
+//@ [index](main.html) | previous | [next](part01.html)