vec is finished

practical.yml

@@ -44,3 +44,18 @@ exercises:
     tests:
       - "add_last_two_not_enough"
       - "add_last_two_enough"
+      - "dup_top_empty"
+      - "dup_top_has_value"
+      - "median_already_sorted"
+      - "median_shuffled"
+      - "median_empty"
+  compute:
+    required_files:
+      - "src/vec.rs"
+      - "src/vec/compute.rs"
+    tests:
+      - "compute_empty"
+      - "compute_too_many_ops"
+      - "compute_division_by_zero_push"
+      - "compute_division_by_zero_operation"
+      - "compute_all_ops"

subject_source/src/vec.rs

@@ -1 +1,2 @@
 pub mod access; 
+pub mod compute;

subject_source/src/vec/access.rs

@@ -1,10 +1,37 @@
 /// Add the last two numbers of the input slice.
 ///
-/// If the slice is not large enough, return `None`
-/// If it is, return the computed value in a `Some`
+/// # Return value
+/// `None` if the slice is not large enough
+/// `Some(result)` if the slice has at least 2 elements
 pub fn add_last_two(v: &[f32]) -> Option<f32> {
     match v.last_chunk() {
         Some([a, b]) => Some(a + b),
         None => None,
     }
 }
+
+/// Duplicate the top element from the stack if it exist
+/// (the stack is represented as a Vec with top == last)
+///
+/// # Return value
+/// `Some(())` if the operation succeeded
+/// `None` if not
+pub fn dup_top(v: &mut Vec<f32>) -> Option<()> {
+    match v.last() {
+        Some(last) => {
+            v.push(*last);
+            return Some(());
+        }
+        _ => return None,
+    }
+}
+
+/// Compute the median of a slice in place (if the slice was sorted, it would be the middle element)
+pub fn median(v: &[i32]) -> Option<i32> {
+    let mut tmp = v.to_vec();
+    tmp.sort();
+    match tmp.get(tmp.len() / 2) {
+        Some(&r) => Some(r),
+        None => None,
+    }
+}

subject_source/src/vec/compute.rs

@@ -0,0 +1,48 @@
+pub enum Operation {
+    Push(f32),
+    Binary(Binary),
+}
+
+pub enum Binary {
+    Add,
+    Sub,
+    Mul,
+    Div,
+}
+
+#[derive(PartialEq, Debug)]
+pub enum ComputeError {
+    NotEnoughData,
+    DivisionByZero,
+}
+
+pub fn compute(operations: &[Operation]) -> Result<f32, ComputeError> {
+    let mut stack = vec![];
+    for operation in operations {
+        match operation {
+            Operation::Push(n) => stack.push(*n),
+            Operation::Binary(op) => {
+                let b = stack.pop();
+                let a = stack.pop();
+
+                let r = match (a, b) {
+                    (Some(a), Some(b)) => match op {
+                        Binary::Add => a + b,
+                        Binary::Mul => a * b,
+                        Binary::Div => {
+                            if b == 0.0 {
+                                return Err(ComputeError::DivisionByZero);
+                            }
+                            a / b
+                        }
+                        Binary::Sub => a - b,
+                    },
+                    _ => return Err(ComputeError::NotEnoughData),
+                };
+                stack.push(r);
+            }
+        }
+    }
+
+    stack.pop().ok_or(ComputeError::NotEnoughData)
+}

subject_source/tests/vec_access.rs

@@ -9,3 +9,31 @@ pub fn add_last_two_not_enough() {
 pub fn add_last_two_enough() {
     assert_eq!(access::add_last_two(&[1.0, 2.0, 3.0]), Some(5.0));
 }
+
+#[test]
+pub fn dup_top_empty() {
+    let mut empty = vec![];
+    assert!(access::dup_top(&mut empty).is_none());
+}
+
+#[test]
+pub fn dup_top_has_values() {
+    let mut empty = vec![1.0, 2.0];
+    assert!(access::dup_top(&mut empty).is_some());
+    assert_eq!(empty, &[1.0, 2.0, 2.0]);
+}
+
+#[test]
+pub fn median_already_sorted() {
+    assert_eq!(access::median(&[1, 2, 3]), Some(2));
+}
+
+#[test]
+pub fn median_shuffled() {
+    assert_eq!(access::median(&[420, 69, 128]), Some(128));
+}
+
+#[test]
+pub fn median_empty() {
+    assert_eq!(access::median(&[]), None);
+}

subject_source/tests/vec_compute.rs

@@ -0,0 +1,58 @@
+use subject_source::vec::compute::*;
+
+#[test]
+pub fn compute_empty() {
+    assert_eq!(compute(&[]), Err(ComputeError::NotEnoughData));
+}
+
+#[test]
+pub fn compute_too_many_ops() {
+    assert_eq!(
+        compute(&[Operation::Push(1.0), Operation::Binary(Binary::Add)]),
+        Err(ComputeError::NotEnoughData)
+    );
+}
+
+#[test]
+pub fn compute_division_by_zero_push() {
+    assert_eq!(
+        compute(&[
+            Operation::Push(1.0),
+            Operation::Push(0.0),
+            Operation::Binary(Binary::Div)
+        ]),
+        Err(ComputeError::DivisionByZero)
+    );
+}
+
+#[test]
+pub fn compute_division_by_zero_operation() {
+    assert_eq!(
+        compute(&[
+            Operation::Push(1.0),
+            Operation::Push(1.0),
+            Operation::Push(1.0),
+            Operation::Binary(Binary::Sub),
+            Operation::Binary(Binary::Div)
+        ]),
+        Err(ComputeError::DivisionByZero)
+    );
+}
+
+#[test]
+pub fn compute_all_ops() {
+    assert_eq!(
+        compute(&[
+            Operation::Push(1.0),
+            Operation::Push(3.0),
+            Operation::Push(2.0),
+            Operation::Binary(Binary::Sub),
+            Operation::Push(5.0),
+            Operation::Binary(Binary::Mul),
+            Operation::Binary(Binary::Add),
+            Operation::Push(2.0),
+            Operation::Binary(Binary::Div),
+        ]),
+        Ok(3.0),
+    );
+}

subject_text/vec/access.md

@@ -0,0 +1,66 @@
+---
+name = "Accessing values"
+file = "src/vec/access.rs"
+---
+
+Instead of using the good old C-style bound checking:
+
+```rust
+if vec.len() < 1 {
+    return None;
+} else {
+    // compiler still thinks this line can panic
+    return vec[0];
+}
+```
+
+Try to implement these functions using non-panicking methods like [`last`](https://doc.rust-lang.org/std/primitive.slice.html#method.last), [`last_chunk`](https://doc.rust-lang.org/std/primitive.slice.html#method.last_chunk), or [`get`](https://doc.rust-lang.org/std/primitive.slice.html#method.get).
+
+> ## note
+> Don't be afraid of the `get` function prototype, look at the examples, they are fairly simple, it's just that `get` can work on multiple types, allowing for slice indexing as well as single element indexing.
+
+> ## note
+> You may want to look at the [`sort`](https://doc.rust-lang.org/std/primitive.slice.html#method.sort) and [`to_vec`](https://doc.rust-lang.org/std/primitive.slice.html#method.to_vec) functions for the median.
+
+```prototype
+/// Add the last two numbers of the input slice.
+///
+/// # Return value
+/// `None` if the slice is not large enough
+/// `Some(result)` if the slice has at least 2 elements
+pub fn add_last_two(v: &[f32]) -> Option<f32> {
+    unimplemented!()
+}
+
+/// Duplicate the top element from the stack if it exist
+/// (the stack is represented as a Vec with top == last)
+///
+/// # Return value
+/// `Some(())` if the operation succeeded
+/// `None` if not
+pub fn dup_top(v: &mut Vec<f32>) -> Option<()> {
+    unimplemented!()
+}
+
+/// Compute the median of a slice in place (if the slice was sorted, it would be the middle element)
+pub fn median(v: &[i32]) -> Option<i32> {
+    unimplemented!()
+}
+```
+
+```example
+fn main() {
+    assert_eq!(add_last_two(&[]), None);
+    assert_eq!(add_last_two(&[10.0]), None);
+    assert_eq!(add_last_two(&[1.0, 2.0, 3.0]), Some(5.0));
+
+    let mut stack = vec![1.0];
+    assert!(dup_top(&mut stack).is_some());
+    assert_eq!(&stack, &[1.0, 1.0]);
+
+    stack.clear();
+    assert!(dup_top(&mut stack).is_none());
+
+    assert_eq!(median(&[2, 1, 3]), Some(2));
+}
+```

subject_text/vec/index.md

@@ -6,29 +6,8 @@ exercises = ["access.md"]
 
 Let's now look at some functions on [`slice`](https://doc.rust-lang.org/std/primitive.slice.html)s and [`Vec`](https://doc.rust-lang.org/std/vec/struct.Vec.html)s. Instead of manualy checking things we will follow the type system using `Option`s and `Result`s we saw earlier.
 
-```note
-Slices (`[T]`) represent some memory space containing an arbitrary number of elements of type `T`. Since they don't have a size known at compilation time, we can only access them through pointers, commonly `&[T]` (references to slices).
-```
-
-```deepening
-`Vec<T>` can be seen as [owned](https://doc.rust-lang.org/book/ch04-00-understanding-ownership.html) `[T]`, it means that every function working on a `&[T]` can work on a `&Vec<T>`.
-```
-
-```prototype
-/// Add the last two numbers of the input slice.
-///
-/// If the slice is not large enough, return `None`
-/// If it is, return the computed value in a `Some`
-pub fn add_last_two(v: &[f32]) -> Option<f32> {
-    unimplemented!()
-}
-```
-
-```example
-fn main() {
-    assert_eq!(add_last_two(&[]), None);
-    assert_eq!(add_last_two(&[10.0]), None);
-    assert_eq!(add_last_two(&[1.0, 2.0, 3.0]), Some(5.0));
-}
-```
+> ## note
+> Slices (`[T]`) represent some memory space containing an arbitrary number of elements of type `T`. Since they don't have a size known at compilation time, we can only access them through pointers, commonly `&[T]` (references to slices).
 
+> ## deepening
+> `Vec<T>` can be seen as [owned](https://doc.rust-lang.org/book/ch04-00-understanding-ownership.html) `[T]`, it means that every function working on a `&[T]` can work on a `&Vec<T>`.