Updates for TR comments

Chapter04/gadt.rs

@@ -1,5 +1,5 @@
 
-type JSJIT = u64;
+struct JSJIT(u64);
 
 enum JSJITorExpr {
    Jit { label: JSJIT },
@@ -18,7 +18,7 @@ fn jump(l: JSJIT) -> JSJITorExpr
    //jump to compiled code
    //this depends on implementation
    //so we will just leave this as a stub
-   JSJITorExpr::Jit { label: 0 }
+   JSJITorExpr::Jit { label: JSJIT(0) }
 }
 fn eval(e: JSJITorExpr) -> JSJITorExpr
 {
@@ -36,14 +36,14 @@ fn eval(e: JSJITorExpr) -> JSJITorExpr
                let r = eval(*r);
                //call add op codes for possible l,r representations
                //should return wrapped value from above
-               JSJITorExpr::Jit { label: 0 }
+               JSJITorExpr::Jit { label: JSJIT(0) }
             }
             JSExpr::OperatorMul { lexpr: l, rexpr: r } => {
                let l = eval(*l);
                let r = eval(*r);
                //call mul op codes for possible l,r representations
                //should return wrapped value from above
-               JSJITorExpr::Jit { label: 0 }
+               JSJITorExpr::Jit { label: JSJIT(0) }
             }
          }
       }

Chapter04/lifetimes.rs

@@ -15,10 +15,38 @@ impl<'a> Red for Ball<'a> { }
 
 static num: i32 = 5;
 
+struct Context<'s>(&'s mut String);
+
+impl<'s> Context<'s>
+{
+   fn mutate<'c>(&mut self, cs: &'c mut String) -> &'c mut String
+   {
+      let swap_a = self.0.pop().unwrap();
+      let swap_b = cs.pop().unwrap();
+      self.0.push(swap_b);
+      cs.push(swap_a);
+      cs
+   }
+}
+
 fn main()
 {
    let x = 3;
    ground_lifetime(&x);
 
    let obj = Box::new(Ball { diameter: &num }) as Box<Red + 'static>;
+
+   let mut s = "outside string context abc".to_string();
+   {
+      //temporary context
+      let mut c = Context(&mut s);
+      {
+         //further temporary context
+         let mut s2 = "inside string context def".to_string();
+         c.mutate(&mut s2);
+         println!("s2 {}", s2);
+      }
+   }
+   println!("s {}", s);
+
 }

Chapter04/parameters.rs

@@ -56,4 +56,7 @@ fn main()
 
    <Baz as Foo>::f(&b);
    <Baz as Bar>::f(&b);
+
+   f::<Foo>(&b);
+   f::<Bar>(&b);
 }