feat: add functions6.rs and move_semantics6.rs exercises about closures

dev/Cargo.toml

@@ -26,6 +26,8 @@ bin = [
   { name = "functions4_sol", path = "../solutions/02_functions/functions4.rs" },
   { name = "functions5", path = "../exercises/02_functions/functions5.rs" },
   { name = "functions5_sol", path = "../solutions/02_functions/functions5.rs" },
+  { name = "functions6", path = "../exercises/02_functions/functions6.rs" },
+  { name = "functions6_sol", path = "../solutions/02_functions/functions6.rs" },
   { name = "if1", path = "../exercises/03_if/if1.rs" },
   { name = "if1_sol", path = "../solutions/03_if/if1.rs" },
   { name = "if2", path = "../exercises/03_if/if2.rs" },
@@ -60,6 +62,8 @@ bin = [
   { name = "move_semantics4_sol", path = "../solutions/06_move_semantics/move_semantics4.rs" },
   { name = "move_semantics5", path = "../exercises/06_move_semantics/move_semantics5.rs" },
   { name = "move_semantics5_sol", path = "../solutions/06_move_semantics/move_semantics5.rs" },
+  { name = "move_semantics6", path = "../exercises/06_move_semantics/move_semantics6.rs" },
+  { name = "move_semantics6_sol", path = "../solutions/06_move_semantics/move_semantics6.rs" },
   { name = "structs1", path = "../exercises/07_structs/structs1.rs" },
   { name = "structs1_sol", path = "../solutions/07_structs/structs1.rs" },
   { name = "structs2", path = "../exercises/07_structs/structs2.rs" },

exercises/02_functions/README.md

@@ -1,8 +1,9 @@
 # Functions
 
 Here, you'll learn how to write functions and how the Rust compiler can help you debug errors even
-in more complex code.
+in more complex code. You will also learn what is the difference with closures.
 
 ## Further information
 
 - [How Functions Work](https://doc.rust-lang.org/book/ch03-03-how-functions-work.html)
+- [Closures](https://doc.rust-lang.org/book/ch13-01-closures.html)

exercises/02_functions/functions6.rs

@@ -0,0 +1,19 @@
+// functions6.rs
+//
+// Here you can practice special functions called `closures`, that can capture
+// variables of their parent context.
+// Fix the code below to make it compile, without changing the two closure
+// definitions.
+//
+// Execute `rustlings hint functions6` or use the `hint` watch subcommand for
+// some hints.
+
+fn main() {
+  // TODO: ensure the definition of captured variable
+  let closure_1 = |input_var: u32| -> u32 {input_var + outer_var};
+  println!("Closure#1 returns {}", closure_1(5));
+
+  let closure_2 = |input_var| println!("Closure#2 (input_var {})", input_var);
+  closure_2(2);
+  closure_2("5"); // TODO: look at the captured variable type here
+}

exercises/06_move_semantics/move_semantics6.rs

@@ -0,0 +1,25 @@
+// move_semantics6.rs
+//
+// Here you will practice how mutable/immutable borrowing works in the context
+// of a closure.
+//
+// Try to fix this code to make it compile and not panic.
+// You can't change anything except removing 1 line.
+//
+// Execute `rustlings hint move_semantics7` or use the `hint` watch subcommand
+// for a hint.
+
+fn main() {
+  let mut counter = 0;
+
+  let mut increment = || {
+    counter += 1;
+    println!("counter equals {}", counter);
+  };
+
+  increment();
+  let _reborrowed_counter = &counter; // TODO: figure out where to put this borrowing instruction
+  increment();
+
+  assert_eq!(counter, 2);
+}

exercises/README.md

@@ -3,7 +3,7 @@
 | Exercise               | Book Chapter        |
 | ---------------------- | ------------------- |
 | variables              | §3.1                |
-| functions              | §3.3                |
+| functions              | §3.3, §13.1         |
 | if                     | §3.5                |
 | primitive_types        | §3.2, §4.3          |
 | vecs                   | §8.1                |

rustlings-macros/info.toml

@@ -187,6 +187,20 @@ There are two solutions:
 1. Add the `return` keyword before `num * num;`
 2. Remove the semicolon `;` after `num * num`"""
 
+[[exercises]]
+name = "functions6"
+dir = "02_functions"
+test = false
+hint = """
+Hint FIX #1: Closures can capture variables defined in the outer context.
+
+Hint FIX #2: Closures can infer both input and returned types, when they are not
+specified in the signature. But the closure cannot be reused with different
+input types.
+
+Read more about closures in the rust book dedicated section:
+https://doc.rust-lang.org/book/ch13-01-closures.html"""
+
 # IF
 
 [[exercises]]
@@ -391,6 +405,18 @@ The first problem is that `get_char` is taking ownership of the string. So
 Once you've fixed that, `string_uppercase`'s function signature will also need
 to be adjusted."""
 
+[[exercises]]
+name = "move_semantics6"
+dir = "06_move_semantics"
+test = false
+hint = """
+When a closure captures a variable to modify it, it actually borrows that variable
+as a mutable reference. In this exercise, the closure mutably borrows the `counter`
+variable, thus, any attempt to borrow `counter` between closure calls leads to an error.
+
+You cannot immutably borrow a variable if a mutable closure is
+called later in the scope."""
+
 # STRUCTS
 
 [[exercises]]

solutions/02_functions/functions6.rs

@@ -0,0 +1,9 @@
+fn main() {
+    let outer_var = 1;
+    let closure_1 = |input_var: u32| -> u32 { input_var + outer_var };
+    println!("Closure#1 returns {}", closure_1(5));
+
+    let closure_2 = |input_var| println!("Closure#2 (input_var {})", input_var);
+    closure_2(2);
+    closure_2(5);
+}

solutions/06_move_semantics/move_semantics6.rs

@@ -0,0 +1,14 @@
+fn main() {
+    let mut counter = 0;
+
+    let mut increment = || {
+        counter += 1;
+        println!("counter equals {}", counter);
+    };
+
+    increment();
+    increment();
+    let _reborrowed_counter = &counter;
+
+    assert_eq!(counter, 2);
+}