From 87eef0eb20858188744e529fb0c5f1282577b8e4 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Tue, 9 Jun 2015 17:21:34 +0200 Subject: [PATCH 1/1] some work on part 02, and the layout --- Makefile | 2 +- src/main.rs | 4 ++-- src/part00.rs | 34 ++++++++++++++++++---------------- src/part01.rs | 9 +++++---- src/part02.rs | 40 ++++++++++++++++++++++++++++++++++++---- 5 files changed, 62 insertions(+), 27 deletions(-) diff --git a/Makefile b/Makefile index 830ba37..dc3ffb0 100644 --- a/Makefile +++ b/Makefile @@ -4,7 +4,7 @@ all: docs rawsrc .PHONY: docs rawsrc docs: - @docco $(FILES) -l linear + @docco $(FILES) # -l linear rawsrc: @mkdir -p rawsrc diff --git a/src/main.rs b/src/main.rs index 7850a99..fdc8f5f 100644 --- a/src/main.rs +++ b/src/main.rs @@ -42,13 +42,13 @@ // * [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(); diff --git a/src/part00.rs b/src/part00.rs index 7fcbf35..90b04ef 100644 --- a/src/part00.rs +++ b/src/part00.rs @@ -2,8 +2,9 @@ // ====================================== // 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 @@ -16,18 +17,18 @@ use std; // 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` 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) -> 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; @@ -42,12 +43,12 @@ fn vec_min(vec: Vec) -> NumberOrNothing { // 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); } @@ -58,18 +59,20 @@ fn vec_min(vec: Vec) -> NumberOrNothing { } // 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 { 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! @@ -77,18 +80,17 @@ fn read_vec() -> Vec { // 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: "), 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); diff --git a/src/part01.rs b/src/part01.rs index 7d66385..7603c1f 100644 --- a/src/part01.rs +++ b/src/part01.rs @@ -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 } } @@ -42,10 +42,11 @@ fn number_or_default(n: NumberOrNothing, default: i32) -> i32 { fn vec_min(v: &Vec) -> 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) @@ -63,7 +64,7 @@ fn vec_min(v: &Vec) -> NumberOrNothing { // 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 { diff --git a/src/part02.rs b/src/part02.rs index 32fbe0a..72dcddc 100644 --- a/src/part02.rs +++ b/src/part02.rs @@ -7,11 +7,11 @@ use std; // 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 { Something(T), Nothing, @@ -25,4 +25,36 @@ use self::SomethingOrNothing::{Something,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` and `Option`. 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 `` +// as *declaring* a type variable ("I am doing something for all types `T`"), and the second `` as +// *using* that variable ("The thing I do, is implement `SomethingOrNothing`"). +impl SomethingOrNothing { + fn new(o: Option) -> Self { + panic!("Not yet implemented."); + } + + fn to_option(self) -> Option { + panic!("Not yet implemented."); + } +} +// Inside an `impl`, `Self` refers to the type we are implementing things for. Here, it is +// an alias for `SomethingOrNothing`. +// 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 { + SomethingOrNothing::new(Some(x)) +} + + +// [index](main.html) | [previous](part01.html) | next -- 2.30.2