X-Git-Url: https://git.ralfj.de/rust-101.git/blobdiff_plain/315bf91eb0b309b29c732ca7726df1f6ca9f567e..229b86d07e94cd3ec175051a44b3f3cb45b40b65:/src/part01.rs?ds=inline

diff --git a/src/part01.rs b/src/part01.rs
index 1603c14..bb3e919 100644
--- a/src/part01.rs
+++ b/src/part01.rs
@@ -1,14 +1,13 @@
 // 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!
 
+// ## 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.
@@ -34,8 +33,15 @@ fn number_or_default(n: NumberOrNothing, default: i32) -> i32 {
     }
 }
 
-// With this fresh knowledge, let us now refactor `vec_min`.
+// 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 {
         // Notice that all we do here is compute a new value for `min`, and that it will always end
@@ -43,7 +49,7 @@ fn vec_min(v: Vec<i32>) -> NumberOrNothing {
         // can express this uniformity.
         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
@@ -55,6 +61,7 @@ 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.
 
+// ## 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
@@ -87,8 +94,8 @@ pub fn main() {
 // 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)