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[rust-101.git] / src / part01.rs

diff --git a/src/part01.rs b/src/part01.rs
index 7d66385f4a53970518cb2a06ae995f623e5d0523..bb3e919f980bc3e4794c2c3a8942aaa31985d08f 100644 (file)
--- a/src/part01.rs
+++ b/src/part01.rs
@@ -1,20 +1,19 @@
 // Rust-101, Part 01: Expressions, Inherent methods
 // ================================================
 
 // Rust-101, Part 01: Expressions, Inherent methods
 // ================================================
 

-use std;
-

 // Even though our code from the first part works, we can still learn a
 // lot by making it prettier. To understand how, it is important to
 // understand that Rust is an "expression-based" language. This means that most of the
 // terms you write down are not just *statements* (executing code), but *expressions*
 // (returning a value). This applies even to the body of entire functions!
 // Even though our code from the first part works, we can still learn a
 // lot by making it prettier. To understand how, it is important to
 // understand that Rust is an "expression-based" language. This means that most of the
 // terms you write down are not just *statements* (executing code), but *expressions*
 // (returning a value). This applies even to the body of entire functions!

-// 
+
+// ## Expression-based programming

 // For example, consider `sqr`:
 fn sqr(i: i32) -> i32 { i * i }
 // Between the curly braces, we are giving the *expression* that computes the return value.
 // So we can just write `i * i`, the expression that returns the square if `i`!
 // This is very close to how mathematicians write down functions (but with more types).
 // For example, consider `sqr`:
 fn sqr(i: i32) -> i32 { i * i }
 // Between the curly braces, we are giving the *expression* that computes the return value.
 // So we can just write `i * i`, the expression that returns the square if `i`!
 // This is very close to how mathematicians write down functions (but with more types).

-// 
+

 // Conditionals are also just expressions. You can compare this to the ternary `? :` operator
 // from languages like C.
 fn abs(i: i32) -> i32 { if i >= 0 { i } else { -i } }
 // Conditionals are also just expressions. You can compare this to the ternary `? :` operator
 // from languages like C.
 fn abs(i: i32) -> i32 { if i >= 0 { i } else { -i } }


@@ -34,21 +33,23 @@ fn number_or_default(n: NumberOrNothing, default: i32) -> i32 {
     }
 }
 
     }
 }
 

-// With this fresh knowledge, let us now refactor `vec_min`. First of all, we are doing a small change
-// to the type: `&Vec<i32>` denotes a *reference* to a `Vec<i32>`. You can think of this as a pointer
-// (in C terms): Arguments in Rust are passed *by value*, so we need to employ explicit references if
-// that's not what we want. References are per default immutable (like variables), a mutable reference
-// would be denoted `&mut Vec<i32>`.
-fn vec_min(v: &Vec<i32>) -> NumberOrNothing {
+// Let us now refactor `vec_min`.
+fn vec_min(v: Vec<i32>) -> NumberOrNothing {
+    // Remember that helper function `min_i32`? Rust allows us to define such helper functions *inside* other
+    // functions. This is just a matter of namespacing, the inner function has no access to the data of the outer
+    // one. Still, being able to nicely group functions can be very useful.
+    fn min_i32(a: i32, b: i32) -> i32 {
+        if a < b { a } else { b }
+    }
+

     let mut min = Nothing;
     for e in v {
     let mut min = Nothing;
     for e in v {

-        let e = *e;

         // Notice that all we do here is compute a new value for `min`, and that it will always end
         // up being a `Number` rather than `Nothing`. In Rust, the structure of the code
         // Notice that all we do here is compute a new value for `min`, and that it will always end
         // up being a `Number` rather than `Nothing`. In Rust, the structure of the code

-        // can express this uniformity as follows:
+        // can express this uniformity.

         min = Number(match min {
             Nothing => e,
         min = Number(match min {
             Nothing => e,

-            Number(n) => std::cmp::min(n, e)
+            Number(n) => min_i32(n, e)

         });
     }
     // The `return` keyword exists in Rust, but it is rarely used. Instead, we typically
         });
     }
     // The `return` keyword exists in Rust, but it is rarely used. Instead, we typically


@@ -60,10 +61,11 @@ fn vec_min(v: &Vec<i32>) -> NumberOrNothing {
 // Now that's already much shorter! Make sure you can go over the code above and actually understand
 // every step of what's going on.
 
 // Now that's already much shorter! Make sure you can go over the code above and actually understand
 // every step of what's going on.
 

+// ## Inherent implementations

 // So much for `vec_min`. Let us now reconsider `print_number_or_nothing`. That function
 // really belongs pretty close to the type `NumberOrNothing`. In C++ or Java, you would
 // probably make it a method of the type. In Rust, we can achieve something very similar
 // So much for `vec_min`. Let us now reconsider `print_number_or_nothing`. That function
 // really belongs pretty close to the type `NumberOrNothing`. In C++ or Java, you would
 // probably make it a method of the type. In Rust, we can achieve something very similar

-// by providing an *inherent implementation* as follows:
+// by providing an *inherent implementation*.

 impl NumberOrNothing {
     fn print(self) {
         match self {
 impl NumberOrNothing {
     fn print(self) {
         match self {


@@ -84,15 +86,16 @@ impl NumberOrNothing {
 fn read_vec() -> Vec<i32> {
     vec![18,5,7,2,9,27]
 }
 fn read_vec() -> Vec<i32> {
     vec![18,5,7,2,9,27]
 }

-pub fn part_main() {
+pub fn main() {

     let vec = read_vec();
     let vec = read_vec();

-    let min = vec_min(&vec);
+    let min = vec_min(vec);

     min.print();
 }
 // You will have to replace `part00` by `part01` in the `main` function in
 // `main.rs` to run this code.
 
     min.print();
 }
 // You will have to replace `part00` by `part01` in the `main` function in
 // `main.rs` to run this code.
 

-// **Exercise**: Write a funtion `vec_avg` that computes the average value of a `Vec<i32>`.
-// *Hint*: `vec.len()` returns the length of a vector `vec`.
+// **Exercise 01.1**: Write a funtion `vec_sum` that computes the sum of all values of a `Vec<i32>`.
+
+// **Exercise 01.2**: Write a function `vec_print` that takes a vector and prints all its elements.

 
 // [index](main.html) | [previous](part00.html) | [next](part02.html)
 
 // [index](main.html) | [previous](part00.html) | [next](part02.html)