feature: added exercise to "traits" chapter

exercises/traits/traits6.rs

@@ -0,0 +1,76 @@
+// traits6.rs
+//
+// Your task is to replace the '??' sections so the code compiles.
+// Don't change any line other than the marked one.
+// Execute `rustlings hint traits6` or use the `hint` watch subcommand for a hint.
+
+// I AM NOT DONE
+
+use std::fmt::{self, Debug, Formatter};
+
+/// Struct representing a house
+#[derive(Default)]
+struct House {
+    area_sqft: u32,
+    purchase_date: String,
+}
+
+/// Struct representing a vehicle
+#[derive(Default)]
+struct Vehicle {
+    name: String,
+    model: String,
+    purchase_date: String,
+}
+
+trait Details {
+    fn summary(&self) -> String;
+}
+
+impl Details for House {
+    fn summary(&self) -> String {
+        format!(
+            "The house has an area of {} sqft and was purchased on {}",
+            self.area_sqft, self.purchase_date
+        )
+    }
+}
+impl Details for Vehicle {
+    fn summary(&self) -> String {
+        format!(
+            "The {} vehicle with model {} was purchased on {}",
+            self.name, self.model, self.purchase_date
+        )
+    }
+}
+
+// TODO: Complete the code
+fn foo(flag: bool) -> ?? {
+    if flag {
+        Box::new(House {
+            area_sqft: 5000,
+            purchase_date: "21 Nov 2017".to_string(),
+        })
+    } else {
+        Box::new(Vehicle {
+            name: "BMW".to_string(),
+            model: "320d".to_string(),
+            purchase_date: "13 Aug 2022".to_string(),
+        })
+    }
+}
+
+impl Debug for dyn Details {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+    // print the summary of the struct returned from the function `foo`
+        write!(f, "{}", ??) // TODO: Complete the code
+    }
+}
+
+pub fn main() {
+    let x = foo(true);
+    println!("{:?}", x);
+    // TODO: Complete the code
+    // print the summary of the struct returned from the function `foo`
+    println!("{}", ??);
+}

info.toml

@@ -737,6 +737,21 @@ To ensure a parameter implements multiple traits use the '+ syntax'. Try replaci
 See the documentation at: https://doc.rust-lang.org/book/ch10-02-traits.html#specifying-multiple-trait-bounds-with-the--syntax
 """
 
+[[exercises]]
+name = "traits6"
+path = "exercises/traits/traits6.rs"
+mode = "compile"
+hint = """
+To ensure a function is able to return incompatible types can be done by using a trait bound that is common to them.
+Wrap the shared trait (implemented by the 2 struct types/objects) as a Boxed trait object. Try replacing the '??' with Box<_> 
+See the documentation at: https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits
+
+Also, in order to make the function printable on console using `:?` symbol. Use the `Debug` trait for the `Details` trait.
+Here, the trait object has to implement `Debug` trait, otherwise the function returning trait object will 
+not be printable on console using {:?} symbol.
+See the documentation at: https://doc.rust-lang.org/std/fmt/trait.Debug.html
+"""
+
 # QUIZ 3
 
 [[exercises]]