Update practicalSession-4.md

practicalSession-4.md

@@ -8,12 +8,18 @@ But, quality also comes with the programming language itself.
 During the last years, Rust emerged as the programming language to build (more) robust, safe software systems (compared to C++ and C).
 Mozilla created Rust to replace C++ in the development of Firefox. Their goal is to have a language more focused on memory access and errors.
 
-Rust has no garbage collector, compiles to native code.
+Rust has no garbage collector at run time, compiles to native code, and you do not have to delete pointers:
+the memory model of rust is defined such a way the compiler can infer where pointers muste be freed. Mozilla created Rust to limit memory issues and attacks on Firefox.
+
+See: https://9to5google.com/2022/12/01/android-memory-safety-rust/
+
+
 
 
 Rust may make C++ and C deprecated during the coming decade(s).
 
 
+
 ## Installation
 
 Rust installer: https://rustup.rs
@@ -32,6 +38,36 @@ You can also run Rust code directly on:
 https://play.rust-lang.org/
 
 
+## A first example
+
+Copy the following code in https://play.rust-lang.org/ and run
+
+```rs
+fn main() {
+    let mut vec0: Vec<i32> = Vec::new();
+    
+    vec0.push(1);
+
+
+    println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0);
+
+    vec0.push(88);
+
+    println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0);
+}
+
+fn foo(_: Vec<i32>) {
+    
+}
+```
+
+Now adds `foo(vec0);` before `vec0.push(88);` 
+
+It does not compile anymore. Not there is no delete keyword.
+`vec0` is given to `foo` so that is does not belong to `main` after the call to `foo`.
+At the end of `foo` the Rust compiler automatically deletes `vec0` at its end since it is not used anymore by this method.
+Contrary to C and C++, Rust puts a strong effort on object scoping so that the compiler knows where objects life end.
+
 
 ## Running Rustlings, the Rust tutorials
 
@@ -52,6 +88,7 @@ Focus on code quality:
 - You can skip the exercises on primitive types (by removing `// I AM NOT DONE`) as these are very simple and not related to the course.
 - `vecs2.rs`. Rust has pointers as in C++/C. Why the second function (the one that uses `map`) should be used instead of the first one? (still related to mutability)
 - `move_semantics1.rs`. As suggested by the *hint* command, why the code does not compile if you put `println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0);` after the call to `fill_vec`? For that read: https://doc.rust-lang.org/stable/rust-by-example/scope/move.html On this point Rust strongly differs from C++/C: this is not a copied argument.
+- You can skip `move_semantics3.rs`, `move_semantics4.rs`, `move_semantics6.rs`