feat: mutable and immutable refs

Author: AbdulxaqDev

notes.txt

@@ -272,4 +272,35 @@
     let mut s = String::from("Brendan");
 
     let r1 = &s;
-    let r2 = &mut s;
+    let r2 = &mut s;
+
+ the immutable references are need to be used before initialization of mutable refence.
+ Otherwise it causes error:
+
+ this code failse:
+
+    let mut s = String::from("hello");
+
+    let r1 = &s;
+    let r2 = &s;
+
+    println!("{} and {}", r1, r2); 
+
+    let r3 = &mut s;
+
+    println!("{}", r2); // here r2, immutable ref is being used after muatble
+
+    println!("{}", r3);
+
+ this code works:
+
+    let mut s = String::from("hello");
+
+    let r1 = &s;
+    let r2 = &s;
+
+    println!("{} and {}", r1, r2); 
+
+    let r3 = &mut s;
+
+    println!("{}", r3);

projects/ownership/src/main.rs

@@ -1,8 +1,10 @@
 fn main() {
-    let mut s = String::from("Brendan");
-
+    let mut s = String::from("hello");
     let r1 = &s;
-    let r2 = &mut s;
-    
-    println!("{}, {}", r1, r2);
+    let r2 = &s;
+
+    println!("{} and {}", r1, r2); 
+
+    let r3 = &mut s;
+    println!("{}", r3);
 }