Edit the std-types segment

Cargo.toml

@@ -6,6 +6,7 @@ members = [
   "src/language-features",
   "src/tuples-and-arrays",
   "src/user-defined-types",
+  "src/std-types",
   "src/exercises",
   "src/bare-metal/useful-crates/allocator-example",
   "src/bare-metal/useful-crates/zerocopy-example",

src/SUMMARY.md

@@ -61,12 +61,14 @@
   - [Exercise: Expression Evaluation](user-defined-types/exercise.md)
     - [Solution](user-defined-types/solution.md)
 - [Standard Library Types](std-types.md)
+  - [Standard Library](std-types/std.md)
   - [Option](std-types/option.md)
   - [Result](std-types/result.md)
   - [String](std-types/string.md)
   - [Vec](std-types/vec.md)
   - [HashMap](std-types/hashmap.md)
-  - [Exercise: Book Reviews](std-types/exercise.md)
+  - [Exercise: Hash Set](std-types/exercise.md)
+    - [Solution](std-types/solution.md)
 
 ----
 
@@ -291,8 +293,6 @@
 ----
 
 - [Solutions](exercises/solutions.md)
-  - [Day 1 Afternoon](exercises/day-1/solutions-afternoon.md)
-  - [Day 2 Morning](exercises/day-2/solutions-morning.md)
   - [Day 2 Afternoon](exercises/day-2/solutions-afternoon.md)
   - [Day 3 Morning](exercises/day-3/solutions-morning.md)
   - [Day 3 Afternoon](exercises/day-3/solutions-afternoon.md)

src/exercises/Cargo.toml

@@ -8,10 +8,6 @@ publish = false
 name = "luhn"
 path = "day-1/luhn.rs"
 
-[[bin]]
-name = "book-library"
-path = "day-2/book-library.rs"
-
 [[bin]]
 name = "strings-iterators"
 path = "day-2/strings-iterators.rs"

src/std-types.md

@@ -7,4 +7,4 @@ In this segment:
 * [String](std-types/string.md)
 * [Vec](std-types/vec.md)
 * [HashMap](std-types/hashmap.md)
-* [Exercise: Book Reviews](std-types/exercise.md)
+* [Exercise: Hash Set](std-types/exercise.md)

src/std-types/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "std-types"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[[bin]]
+name = "hashset"
+path = "exercise.rs"

src/std-types/exercise.md

@@ -1,56 +1,56 @@
 ---
 minutes: 5
-existing course material:
-- exercises/day-2/book-library.md
 ---
 
-<!-- NOTES:
-Inspired by example from https://doc.rust-lang.org/std/collections/struct.HashMap.html with one bit missing
--->
-# Exercise: Book Reviews
-
-# Storing Books
-
-We will learn much more about structs and the `Vec<T>` type tomorrow. For now,
-you just need to know part of its API:
-
-```rust,editable
-fn main() {
-    let mut vec = vec![10, 20];
-    vec.push(30);
-    let midpoint = vec.len() / 2;
-    println!("middle value: {}", vec[midpoint]);
-    for item in &vec {
-        println!("item: {item}");
-    }
-}
-```
-
-Use this to model a library's book collection. Copy the code below to
-<https://play.rust-lang.org/> and update the types to make it compile:
+# Exercise: Hash Set
 
-```rust,should_panic
-{{#include exercise.rs:setup}}
-{{#include exercise.rs:Library_new}}
-        todo!("Initialize and return a `Library` value")
-    }
+In this exercise you will build a very simple hash set that stores `u32` values.
+The hash set will have a fixed size, and buckets should be selected with a
+simple modulus operation (`i % num_buckets`). Use a `Vec` to represent each
+bucket (separate chaining). Hint: a vector can contain other vectors:
+`Vec<Vec<u32>>`.
 
-{{#include exercise.rs:Library_len}}
+While solving this exercise, you may encounter a few "rough edges". The error
+messages from the compiler may help you to solve these, but if not, don't
+`panic!` -- discuss them with your classmates or instructor.
 
-{{#include exercise.rs:Library_is_empty}}
+```rust
+// TODO: define a type IntegerHashSet.
+struct IntegerHashSet;
 
-{{#include exercise.rs:Library_add_book}}
-
-{{#include exercise.rs:Library_print_books}}
+{{#include exercise.rs:new}}
+    todo!()
+}
 
-{{#include exercise.rs:Library_oldest_book}}
+{{#include exercise.rs:test_membership}}
+    todo!()
 }
 
-{{#include exercise.rs:main}}
+{{#include exercise.rs:tests}}
 ```
 
+If you finish early, try to adjust the hash set to use open addressing. What
+happens if all of the give integers do not fit?
+
 <details>
 
-[Solution](solutions-afternoon.md#designing-a-library)
+The rough edges are present partially because it's hard to do "interesting"
+things in Rust without references, and partially because responding to the Rust
+compiler's errors is an important skill to practice.
+
+Highlight that students should not suffer the rough edges silently.
+
+ * The hashset is passed by reference, but we haven't yet covered references.
+   This is done in the provided code, so should not cause errors for students.
+
+ * The integers are `u32` but the size of the hash table is a `usize`, so values
+   must be cast. Can we be sure those casts are correct?
+
+ * Depending on how students implement iteration, they may run into ownership
+   issues. For example, `for elt in hashset.buckets[b]` will move the bucket.
+   The compiler will suggest `for elt in &hashset.buckets[b]`, but then `elt`
+   has type `&u32`, so students must write `*elt`.
+     * Consider this a kind of foreshadowing of memory and borrows on day 3.
+     * The `Vec::contains` method may avoid the need for a `for` loop.
 
 </details>