From: Ralf Jung <post@ralfj.de>
Date: Tue, 9 Jun 2015 09:21:12 +0000 (+0200)
Subject: start in part 02
X-Git-Url: https://git.ralfj.de/rust-101.git/commitdiff_plain/53260b4082f1c76b657845560c273b853a166fab

start in part 02
---

diff --git a/src/main.rs b/src/main.rs
index 09a16d1..7850a99 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -39,11 +39,13 @@
 // [the first part](part00.html), or jump directly to where you left off:
 // 
 // * [Part 00](part00.html)
-// * [Part 01](part01.html) (WIP)
+// * [Part 01](part01.html)
+// * [Part 02](part02.html) (WIP)
 // * (to be continued)
 #![allow(dead_code)]
 mod part00;
 mod part01;
+mod part02;
 
 // To actually run the code of some part (after filling in the blanks, if necessary), simply edit the `main`
 // function below.
diff --git a/src/part01.rs b/src/part01.rs
index 36e15d0..7c205bd 100644
--- a/src/part01.rs
+++ b/src/part01.rs
@@ -1,4 +1,4 @@
-// Rust-101, Part 00: Expressions, Inherent methods
+// Rust-101, Part 01: Expressions, Inherent methods
 // ================================================
 
 use std;
@@ -8,13 +8,13 @@ use std;
 // 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!
-
+// 
 // 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 } }
@@ -92,4 +92,7 @@ pub fn part_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`.
+
 // [index](main.html) | [previous](part00.html) | [next](part02.html)
diff --git a/src/part02.rs b/src/part02.rs
new file mode 100644
index 0000000..32fbe0a
--- /dev/null
+++ b/src/part02.rs
@@ -0,0 +1,28 @@
+// Rust-101, Part 02: Generic types (WIP)
+// ================================
+
+use std;
+
+// Let us for a moment reconsider the type `NumberOrNothing`. Isn't it a bit
+// annoying that we had to hard-code the type `i32` in there? What if tomorrow,
+// we want a `CharOrNothing`, and later a `FloatOrNothing`? Certainly we don't
+// want to re-write the type and all its inherent methods.
+// 
+// The solution to this is called *generics* or *polymorphism* (the latter is Greek,
+// meaning "many shapes"). You may know something similar from C++ (where it's called
+// *templates*) or Java, or one of the many functional languages. A generic
+// `SomethingOrNothing` type looks as follows:
+enum SomethingOrNothing<T>  {
+    Something(T),
+    Nothing,
+}
+use self::SomethingOrNothing::{Something,Nothing};
+// What this does is to define an entire family of types: We can now write
+// `SomethingOrNothing<i32>` to get back our `NumberOrNothing`, but we
+// can also write `SomethingOrNothing<bool>` or even `SomethingOrNothing<SomethingOrNothing<i32>>`.
+// In fact, such a type is so useful that it is already present in the standard
+// library: It's called an *option type*, written `Option<T>`.
+// Go check out its [documentation](http://doc.rust-lang.org/stable/std/option/index.html)!
+// (And don't worry, there's indeed lots of material mentioned there that we did not cover yet.)
+
+// [index](main.html) | [previous](part01.html) | [next](part03.html)