feat: Add example about wrapper pattern, Also fix missing example for associated types in trait

traits/traits_2/src/main.rs

@@ -1,48 +1,14 @@
-mod calculation_spec;
-mod two_dimensional;
+use std::fmt::{write, Display};
 
-use crate::calculation_spec::Area;
+struct Wrapper(Vec<String>);
 
-fn main() {
-    // let circle_one = two_dimensional::Circle{ radius: 10 };
-    let circle_one = new_circle(5);
-    // println!("circle area: {}", circle_one.calculate());
-    calculate_and_print_result("circle".to_string(), &circle_one);
-
-    // let square_one = two_dimensional::Square{ length: 5 };
-    let square_one = new_square(10);
-    // println!("square area: {}", square_one.calculate());
-    calculate_and_print_result("square".to_string(), &square_one);
-}
-
-fn new_circle(radius: i32) -> impl Area {
-    let data = two_dimensional::Circle{
-        radius
-    };
-    data
-}
-
-fn new_square(length: i32) -> impl Area {
-    two_dimensional::Square{
-        length
+impl Display for Wrapper {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write(f, format_args!("{:?}", self.0))
     }
 }
 
-fn calculate_and_print_result(name: String, item: &impl Area) {
-    println!("{} area: {}", name, item.calculate());
-}
-
-fn calculate_and_print_result2<T: Area>(name: String, item: &T) {
-    println!("{} area: {}", name, item.calculate());
-}
-
-fn calculate_and_print_result3<T>(name: String, item: &T) where T: Area {
-    println!("{} area: {}", name, item.calculate());
+fn main() {
+    let v = Wrapper(vec![String::from("a"), String::from("b")]);
+    println!("{}", v)
 }
-
-fn calculate_and_print_result4<T>(name: String, item: &T)
-where
-    T: Area,
-{
-    println!("{} area: {}", name, item.calculate());
-}

traits/traits_3/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "traits_3"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

traits/traits_3/src/main.rs

@@ -0,0 +1,60 @@
+mod calculation_spec;
+mod two_dimensional;
+
+use crate::calculation_spec::Area;
+
+trait Message {
+    fn log(&self);
+}
+
+impl Message for String {
+    fn log(&self) {
+        println!("{}", self);
+    }
+}
+
+fn main() {
+    let s = String::from("hello");
+    s.log();
+
+    // let circle_one = two_dimensional::Circle{ radius: 10 };
+    let circle_one = new_circle(5);
+    // println!("circle area: {}", circle_one.calculate());
+    calculate_and_print_result("circle".to_string(), &circle_one);
+
+    // let square_one = two_dimensional::Square{ length: 5 };
+    let square_one = new_square(10);
+    // println!("square area: {}", square_one.calculate());
+    calculate_and_print_result("square".to_string(), &square_one);
+}
+
+fn new_circle(radius: i32) -> impl Area {
+    let data = two_dimensional::Circle { radius };
+    data
+}
+
+fn new_square(length: i32) -> impl Area {
+    two_dimensional::Square { length }
+}
+
+fn calculate_and_print_result(name: String, item: &impl Area) {
+    println!("{} area: {}", name, item.calculate());
+}
+
+fn calculate_and_print_result2<T: Area>(name: String, item: &T) {
+    println!("{} area: {}", name, item.calculate());
+}
+
+fn calculate_and_print_result3<T>(name: String, item: &T)
+where
+    T: Area,
+{
+    println!("{} area: {}", name, item.calculate());
+}
+
+fn calculate_and_print_result4<T>(name: String, item: &T)
+where
+    T: Area,
+{
+    println!("{} area: {}", name, item.calculate());
+}

traits/traits_4/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "traits_4"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

traits/traits_4/src/circle.rs

@@ -0,0 +1,11 @@
+pub struct Circle {
+    pub radius: f64,
+}
+
+impl crate::shape::Shape for Circle {
+    type Area = f64;
+
+    fn area(&self) -> Self::Area {
+        std::f64::consts::PI * self.radius * self.radius
+    }
+}

traits/traits_4/src/main.rs

@@ -0,0 +1,14 @@
+mod circle;
+mod shape;
+mod square;
+
+use crate::shape::Shape;
+
+fn main() {
+    let obj1 = circle::Circle { radius: 10.0 };
+    println!("area of circle: {:.2}", obj1.area());
+
+    let obj2 = square::Square { side: 10 };
+    println!("area of square: {:}", obj2.area());
+}
+

traits/traits_4/src/shape.rs

@@ -0,0 +1,5 @@
+pub trait Shape {
+    type Area;
+
+    fn area(&self) -> Self::Area;
+}

traits/traits_4/src/square.rs

@@ -0,0 +1,11 @@
+pub struct Square {
+    pub side: i64,
+}
+
+impl crate::shape::Shape for Square {
+    type Area = i64;
+
+    fn area(&self) -> Self::Area {
+        self.side * self.side
+    }
+}