part 01: references, expressions, inherent impls

diff --git a/src/part00.rs b/src/part00.rs
index 1c7d3ce6839ca051053ba77f3494f8233b25041a..7fcbf3592b87aecf710c9d517b006d353a1ebc74 100644 (file)
--- a/src/part00.rs
+++ b/src/part00.rs
@@ -1,5 +1,5 @@
-// Rust-101, Part 00: Algebraic datatypes, expressions
-// ===================================================
+// Rust-101, Part 00: Algebraic datatypes
+// ======================================

 
 // 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:
 
 // 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:


@@ -26,7 +26,7 @@ enum NumberOrNothing {
 // (growable) arrays of numbers, and we will use that as our list type.
 // Observe how in Rust, the return type comes *after* the arguments.
 
 // (growable) arrays of numbers, and we will use that as our list type.
 // Observe how in Rust, the return type comes *after* the arguments.
 

-fn vec_min_try1(vec: Vec<i32>) -> NumberOrNothing {
+fn vec_min(vec: Vec<i32>) -> NumberOrNothing {

     // First, we 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":
     // First, we 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":


@@ -62,59 +62,13 @@ fn vec_min_try1(vec: Vec<i32>) -> NumberOrNothing {
 // the constructors of `NumberOrNothing` into the local namespace:
 use self::NumberOrNothing::{Number,Nothing};
 // Try moving that above the function, and removing all the occurrences `NumberOrNothing::`.
 // the constructors of `NumberOrNothing` into the local namespace:
 use self::NumberOrNothing::{Number,Nothing};
 // Try moving that above the function, and removing all the occurrences `NumberOrNothing::`.

-// Things should still compile, now being much less verbose!
-
-// There is more prettification we can do. 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!
-
-// 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 } }
-
-// And the same applies to case distinction with `match`: Every `arm` of the match
-// gives the expression that is returned in the respective case.
-fn number_or_default(n: NumberOrNothing, default: i32) -> i32 {
-    match n {
-        Nothing => default,
-        Number(n) => n,
-    }
-}
-
-// With this fresh knowledge, let us now refactor `vec_min`.
-fn vec_min(v: Vec<i32>) -> NumberOrNothing {
-    let mut min = Nothing;
-    for e in v {
-        // First of all, notice that all we do here is compute a new value for `min`, and that it
-        // will always end up being `Number` rather than `Nothing`. In Rust, the structure of the code
-        // can express this uniformity as follows:
-        min = Number(match min {
-            Nothing => e,
-            Number(n) => std::cmp::min(n, e)
-        });
-    }
-    // The `return` keyword exists in Rust, but it is rarely used. Instead, we typically
-    // make use of the fact that the entire function body is an expression, so we can just
-    // write down the desired return value.
-    min
-}
-
-// 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.

 
 // 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:
 
 fn read_vec() -> Vec<i32> {
     vec![18,5,7,1,9,27]
 
 // 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:
 
 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
+    // `vec!` is a *macro* (as you can tell from the `!`) that constructs a constant `Vec<_>` with the given

     // elements.
 }
 
     // elements.
 }
 


@@ -127,6 +81,9 @@ fn print_number_or_nothing(n: NumberOrNothing) {
     match n {
         Nothing => println!("The number is: <nothing>"),
         Number(n) => println!("The number is: {}", n),
     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.

     };
 }
 
     };
 }
 

diff --git a/src/part01.rs b/src/part01.rs
index bd7e9fb769b38e6a03c3915e36d7bd4eb34d7034..36e15d0245941e07de68de0332ec12b823b5ae37 100644 (file)
--- a/src/part01.rs
+++ b/src/part01.rs
@@ -1,10 +1,95 @@
-// [index](main.html) | [previous](part00.html) | [next](part02.html)
+// Rust-101, Part 00: 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!
+
+// 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).

 
 

-// Rust-101, Part 00
-// =================
+// 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 } }
+
+// And the same applies to case distinction with `match`: Every `arm` of the match
+// gives the expression that is returned in the respective case.
+// (We repeat the definition from the previous part here.)
+enum NumberOrNothing {
+    Number(i32),
+    Nothing
+}
+use self::NumberOrNothing::{Number,Nothing};
+fn number_or_default(n: NumberOrNothing, default: i32) -> i32 {
+    match n {
+        Nothing => default,
+        Number(n) => n,
+    }
+}

 
 

+// 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 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
+        // can express this uniformity as follows:
+        min = Number(match min {
+            Nothing => e,
+            Number(n) => std::cmp::min(n, e)
+        });
+    }
+    // The `return` keyword exists in Rust, but it is rarely used. Instead, we typically
+    // make use of the fact that the entire function body is an expression, so we can just
+    // write down the desired return value.
+    min
+}
+
+// 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.
+
+// 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:
+impl NumberOrNothing {
+    fn print(self) {
+        match self {
+            Nothing => println!("The number is: <nothing>"),
+            Number(n) => println!("The number is: {}", n),
+        };
+    }
+}
+// So, what just happened? Rust separates code from data, so the definition of the
+// methods on an `enum` (and also on `struct`, which we will learn about later)
+// is independent of the definition of the type. `self` is like `this` in other
+// languages, and its type is always implicit. So `print` is now a method that
+// takes as first argument a `NumberOrNothing`, just like `print_number_or_nothing`.
+//
+// Try making `number_or_default` from above an inherent method as well!
+
+// With our refactored functions and methods, `main` now looks as follows:
+fn read_vec() -> Vec<i32> {
+    vec![18,5,7,2,9,27]
+}

 pub fn part_main() {
 pub fn part_main() {

-    
+    let vec = read_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.

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