add ownersystem examples

ownership system/ownersystem_1.rs

@@ -0,0 +1,26 @@
+// $ rustc ownersystem_1.rs 
+// $ ./ownersystem_1
+struct Bob {
+    n: Vec<i32>
+}
+
+impl Bob {
+    fn new() -> Bob {
+        Bob { n: Vec::new() }
+    }
+}
+
+fn func_1() {
+    let n = Bob::new();
+    func_2(n);
+    //is now out of scope as func_2 owns n now.
+    //println!("{}", bob.n[0]);
+}
+
+fn func_2(b: Bob) {
+    println!("{}", b.n[0]);
+}
+
+fn main() {
+    func_1();
+}

ownership system/ownersystem_2_borrowing.rs

@@ -0,0 +1,26 @@
+// $ rustc ownersystem_2_borrowing.rs 
+// $ ./ownersystem_2_borrowing
+struct Bob {
+    n: Vec<i32>
+}
+
+impl Bob {
+    fn new() -> Bob {
+        Bob { n: Vec::new() }
+    }
+}
+
+fn func_1() {
+    let n = Bob::new();
+    func_2(&n);
+    //is now in scope as func_2 just got a read only reference.
+    println!("{}", n.n[0]);
+}
+
+fn func_2(b: &Bob) {
+    println!("{}", b.n[0]);
+}
+
+fn main() {
+    func_1();
+}

ownership system/ownersystem_3_borrowing.rs

@@ -0,0 +1,33 @@
+// $ rustc ownersystem_3_borrowing.rs 
+// $ ./ownersystem_3_borrowing
+struct Bob {
+    n: Vec<i32>
+}
+
+impl Bob {
+    fn new() -> Bob {
+        Bob { n: Vec::new() }
+    }
+}
+
+fn func_1() {
+    let n = Bob::new();
+    let n1 = &n;
+    let n2 = &n;
+    func_2(n1);
+    func_3(n2);
+    //works because both func_2 and func_3 only got read only references
+    println!("{}", n.n[0]);
+}
+
+fn func_2(b: &Bob) {
+    println!("{}", b.n[0]);
+}
+
+fn func_3(b: &Bob) {
+    println!("{}", b.n[0]);
+}
+
+fn main() {
+    func_1();
+}

ownership system/ownersystem_4_mutable.rs

@@ -0,0 +1,34 @@
+// $ rustc ownersystem_4_mutable.rs 
+// $ ./ownersystem_4_mutable
+struct Bob {
+    n: Vec<i32>
+}
+
+impl Bob {
+    fn new() -> Bob {
+        Bob { n: Vec::new() }
+    }
+}
+
+fn func_1() {
+    let mut n = Bob::new();
+    let n1 = &mut n;
+    // doesn't work because there is already a mutable borrowing
+    //let n2 = &n;
+    func_2(n1);
+    //func_3(n2);
+    //works because both func_2 and func_3 only got read only references
+    println!("{}", n.n[0]);
+}
+
+fn func_2(b: &mut Bob) {
+    println!("{}", b.n[0]);
+}
+
+fn func_3(b: &Bob) {
+    println!("{}", b.n[0]);
+}
+
+fn main() {
+    func_1();
+}

ownership system/raii.cpp

@@ -0,0 +1,30 @@
+// $ g++ -o raii raii.cpp
+// https://en.wikipedia.org/wiki/Resource_acquisition_is_initialization
+#include <cstdio>
+class MyClass {
+    int *n;
+    public:
+        MyClass(int x)
+        {
+            this->n = new int[x];
+            printf("constructor\n");
+        }
+        ~MyClass()
+        {
+            delete this->n;
+            printf("deconstructor\n");
+        }
+        int* get_n()
+        {
+            return this->n;
+        }
+};
+
+int main()
+{
+    MyClass *b = new MyClass(5);
+    int *xs = b->get_n();
+    printf("%d\n", xs[0]);
+    delete b;
+    printf("%d\n", xs[0]);
+}