.PHONY: docs rawsrc
docs:
- @docco $(FILES) -l linear
+ @docco $(FILES) # -l linear
rawsrc:
@mkdir -p rawsrc
// * [Part 01](part01.html)
// * [Part 02](part02.html) (WIP)
// * (to be continued)
-#![allow(dead_code)]
+#![allow(dead_code, unused_imports, unused_variables)]
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.
+// function.
fn main() {
part00::part_main();
// ======================================
// 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:
+// 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
// 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
}
-
// 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.
+// Observe how in Rust, the return type comes *after* the arguments.
fn vec_min(vec: Vec<i32>) -> NumberOrNothing {
- // First, we need some variable to store the minimum as computed so far.
+ // 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;
// 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 => {
- // In this case (*arm*) of the `match`, `min` is currently nothing, so let's just make it the 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.
NumberOrNothing::Number(n) => {
- // In this arm, `min` is currently the number `n`, so let's compute the new minimum and store it.
let new_min = std::cmp::min(n, el);
min = NumberOrNothing::Number(new_min);
}
}
// Phew. We wrote our first Rust function! But all this `NumberOrNothing::` is getting kind of
-// ugly. Can't we do that nicer? Indeed, we can: The following line tells Rust to take
-// the constructors of `NumberOrNothing` into the local namespace:
-use self::NumberOrNothing::{Number,Nothing};
+// ugly. Can't we do that nicer?
+
+// 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::`.
+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:
+// 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.
fn read_vec() -> Vec<i32> {
vec![18,5,7,1,9,27]
- // `vec!` is a *macro* (as you can tell from the `!`) that constructs a constant `Vec<_>` with the given
- // elements.
}
// Finally, let's call our functions and run the code!
// 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.
fn print_number_or_nothing(n: NumberOrNothing) {
match n {
Nothing => println!("The number is: <nothing>"),
Number(n) => println!("The number is: {}", n),
- // `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.
};
}
// Putting it all together:
-
pub fn part_main() {
let vec = read_vec();
let min = vec_min(vec);
// 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 } }
fn vec_min(v: &Vec<i32>) -> NumberOrNothing {
let mut min = Nothing;
for e in v {
+ // Now that `v` is just a reference, the same goes for `e`, so we have to dereference the pointer.
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
- // can express this uniformity as follows:
+ // can express this uniformity.
min = Number(match min {
Nothing => e,
Number(n) => std::cmp::min(n, e)
// 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 {
// 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:
+// *templates*) or Java, or one of the many functional languages. So here, we define
+// a generic `SomethingOrNothing` type.
enum SomethingOrNothing<T> {
Something(T),
Nothing,
// 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)
+// **Exercise**: Write functions converting between `SomethingOrNothing<T>` and `Option<T>`. You will have to use
+// the names of the constructor of `Option`, which you can find in the documentation I linked above.
+
+// Here's a skeleton for your solution, you only have to fill in the function bodies.
+// (`panic!` is, again, a macro - this one terminates execution when it is reached).
+//
+// Notice the syntax for giving generic implementations to generic types: Think of the first `<T>`
+// as *declaring* a type variable ("I am doing something for all types `T`"), and the second `<T>` as
+// *using* that variable ("The thing I do, is implement `SomethingOrNothing<T>`").
+impl<T> SomethingOrNothing<T> {
+ fn new(o: Option<T>) -> Self {
+ panic!("Not yet implemented.");
+ }
+
+ fn to_option(self) -> Option<T> {
+ panic!("Not yet implemented.");
+ }
+}
+// Inside an `impl`, `Self` refers to the type we are implementing things for. Here, it is
+// an alias for `SomethingOrNothing<T>`.
+// Remember that `self` is the `this` of Rust, and implicitly has type `Self`.
+//
+// Observe how `new` does *not* have a `self` parameter. This corresponds to a `static` method
+// in Java or C++. In fact, `new` is the Rust convention for defining constructors: They are
+// nothing special, just static functions returning `Self`.
+
+// You can call static functions, and in particular constructors, as follows:
+fn call_constructor(x: i32) -> SomethingOrNothing<i32> {
+ SomethingOrNothing::new(Some(x))
+}
+
+
+// [index](main.html) | [previous](part01.html) | next
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