add [Newtype and DST]

ChangeLog.md

@@ -3,6 +3,8 @@
 ## 2022-03-31
 
 - Add [Iterator](https://practice.rs/functional-programing/iterator.html)
+- Add [Newtype and DST](https://practice.rs/newtype-sized.html)
+
 
 ## 2022-03-30
 

en/src/SUMMARY.md

@@ -56,7 +56,7 @@
 - [Functional programing](functional-programing/intro.md)
   - [Closure](functional-programing/cloure.md)
   - [Iterator](functional-programing/iterator.md)
-- [newtype and Sized TODO](newtype-sized.md)
+- [newtype and DST](newtype-sized.md)
 - [Smart pointers TODO](smart-pointers/intro.md)
   - [Box](smart-pointers/box.md)
   - [Deref](smart-pointers/deref.md)

en/src/newtype-sized.md

@@ -1 +1,204 @@
 # newtype and Sized
+
+## Newtype
+The orphan rule tells us that we are allowed to implement a trait on a type as long as either the trait or the type are local to our crate.
+
+The **newtype pattern** can help us get around this restriction, which involves creating a new type in a **tuple struct**.
+
+1、🌟
+```rust,editable
+use std::fmt;
+
+/* Define the Wrapper type */
+__;
+
+// Display is an external trait
+impl fmt::Display for Wrapper {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "[{}]", self.0.join(", "))
+    }
+}
+
+fn main() {
+    // Vec is an external type, so you cannot implement Display trait on Vec type
+    let w = Wrapper(vec![String::from("hello"), String::from("world")]);
+    println!("w = {}", w);
+}
+```
+
+2、🌟 Hide the methods of the orginal type
+```rust,editable
+/* Make it workd */
+struct Meters(u32);
+
+fn main() {
+    let i: u32 = 2;
+    assert_eq!(i.pow(2), 4);
+
+    let n = Meters(i);
+    // The `pow` method is defined on `u32` type, we can't directly call it 
+    assert_eq!(n.pow(2), 4);
+}
+```
+
+3、🌟🌟 The `newtype` idiom gives compile time guarantees that the right type of value is suplied to a program.
+```rust,editable
+/* Make it work */
+struct Years(i64);
+
+struct Days(i64);
+
+impl Years {
+    pub fn to_days(&self) -> Days {
+        Days(self.0 * 365)
+    }
+}
+
+
+impl Days {
+    pub fn to_years(&self) -> Years {
+        Years(self.0 / 365)
+    }
+}
+
+// an age verification function that checks age in years, must be given a value of type Years.
+fn old_enough(age: &Years) -> bool {
+    age.0 >= 18
+}
+
+fn main() {
+    let age = Years(5);
+    let age_days = age.to_days();
+    println!("Old enough {}", old_enough(&age));
+    println!("Old enough {}", old_enough(&age_days));
+}
+```
+
+4、🌟🌟
+```rust,editable
+use std::ops::Add;
+use std::fmt::{self, format};
+
+struct Meters(u32);
+impl fmt::Display for Meters {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "There are still {} meters left", self.0)
+    }
+}
+
+impl Add for Meters {
+    type Output = Self;
+
+    fn add(self, other: Meters) -> Self {
+        Self(self.0 + other.0)
+    }
+}
+fn main() {
+    let d = calculate_distance(Meters(10), Meters(20));
+    assert_eq!(format!("{}",d), "There are still 30 meters left");
+}
+
+/* implement calculate_distance  */
+fn calculate_distance
+```
+
+## Type alias
+The most importance of type alias is to improve the readability of our codes.
+
+```rust
+type Thunk = Box<dyn Fn() + Send + 'static>;
+
+let f: Thunk = Box::new(|| println!("hi"));
+
+fn takes_long_type(f: Thunk) {
+    // --snip--
+}
+
+fn returns_long_type() -> Thunk {
+    // --snip--
+}
+```
+
+```rust
+type Result<T> = std::result::Result<T, std::io::Error>;
+```
+
+And Unlike newtype, type alias don't create new types, so the following code is valid:
+```rust
+type Meters = u32;
+
+let x: u32 = 5;
+let y: Meters = 5;
+
+println!("x + y = {}", x + y);
+```
+
+5、🌟
+```rust,editable
+enum VeryVerboseEnumOfThingsToDoWithNumbers {
+    Add,
+    Subtract,
+}
+
+/* Fill in the blank */
+__
+
+fn main() {
+    // We can refer to each variant via its alias, not its long and inconvenient
+    // name.
+    let x = Operations::Add;
+}
+```
+
+6、🌟🌟 There are a few preserved alias in Rust, one of which can be used in `impl` blocks.
+```rust,editable
+enum VeryVerboseEnumOfThingsToDoWithNumbers {
+    Add,
+    Subtract,
+}
+
+impl VeryVerboseEnumOfThingsToDoWithNumbers {
+    fn run(&self, x: i32, y: i32) -> i32 {
+        match self {
+            __::Add => x + y,
+            __::Subtract => x - y,
+        }
+    }
+}
+```
+
+## DST and unsized type
+These concepts are complicated, so we are not going to explain here, but you can find them in [The Book](https://doc.rust-lang.org/book/ch19-04-advanced-types.html?highlight=DST#dynamically-sized-types-and-the-sized-trait).
+
+7、🌟🌟🌟 Array with dynamic length is a Dynamic Sized Type ( DST ), we can't directly use it
+```rust,editable
+/* Make it work with const generics */
+fn my_function(n: usize) -> [u32; usize] {
+    [123; n]
+}
+
+fn main() {
+    let arr = my_function();
+    println!("{:?}",arr);
+}
+```
+
+8、🌟🌟 Slice is unsized type, but the reference of slice is not.
+```rust,editable
+/* Make it work with slice references */
+fn main() {
+    let s: str = "Hello there!";
+
+    let arr: [u8] = [1, 2, 3];
+}
+```
+
+9、🌟🌟 Trait is also a unsized type
+```rust,editable
+/* Make it work in two ways */
+use std::fmt::Display;
+fn foobar(thing: Display) {}    
+
+fn main() {
+}
+```

solutions/newtype-sized.md

@@ -0,0 +1,162 @@
+1、
+```rust
+use std::fmt;
+
+struct Wrapper(Vec<String>);
+
+impl fmt::Display for Wrapper {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "[{}]", self.0.join(", "))
+    }
+}
+
+fn main() {
+    let w = Wrapper(vec![String::from("hello"), String::from("world")]);
+    println!("w = {}", w);
+}
+```
+
+2、
+```rust
+struct Meters(u32);
+
+fn main() {
+    let i: u32 = 2;
+    assert_eq!(i.pow(2), 4);
+
+    let n = Meters(i);
+    assert_eq!(n.0.pow(2), 4);
+}
+```
+
+3、
+```rust
+struct Years(i64);
+
+struct Days(i64);
+
+impl Years {
+    pub fn to_days(&self) -> Days {
+        Days(self.0 * 365)
+    }
+}
+
+
+impl Days {
+    pub fn to_years(&self) -> Years {
+        Years(self.0 / 365)
+    }
+}
+
+// an age verification function that checks age in years, must be given a value of type Years.
+fn old_enough(age: &Years) -> bool {
+    age.0 >= 18
+}
+
+fn main() {
+    let age = Years(5);
+    let age_days = age.to_days();
+    println!("Old enough {}", old_enough(&age));
+    println!("Old enough {}", old_enough(&age_days.to_years()));
+}
+```
+
+4、Sometimes `newtype` pattern can provide extra readability.
+```rust
+use std::ops::Add;
+use std::fmt::{self, format};
+
+struct Meters(u32);
+impl fmt::Display for Meters {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "There are still {} meters left", self.0)
+    }
+}
+
+impl Add for Meters {
+    type Output = Self;
+
+    fn add(self, other: Meters) -> Self {
+        Self(self.0 + other.0)
+    }
+}
+fn main() {
+    let d = calculate_distance(Meters(10), Meters(20));
+    assert_eq!(format!("{}",d), "There are still 30 meters left");
+}
+
+/* implement calculate_distance  */
+fn calculate_distance(d1: Meters, d2: Meters) -> Meters {
+    d1 + d2
+}
+```
+
+5、
+```rust
+enum VeryVerboseEnumOfThingsToDoWithNumbers {
+    Add,
+    Subtract,
+}
+
+/* Fill in the blank */
+type Operations = VeryVerboseEnumOfThingsToDoWithNumbers;
+
+fn main() {
+    // We can refer to each variant via its alias, not its long and inconvenient
+    // name.
+    let x = Operations::Add;
+}
+```
+
+6、
+```rust
+enum VeryVerboseEnumOfThingsToDoWithNumbers {
+    Add,
+    Subtract,
+}
+
+impl VeryVerboseEnumOfThingsToDoWithNumbers {
+    fn run(&self, x: i32, y: i32) -> i32 {
+        match self {
+            Self::Add => x + y,
+            Self::Subtract => x - y,
+        }
+    }
+}
+
+fn main() {
+    
+}
+```
+
+7、
+```rust
+fn my_function<const N: usize>() -> [u32; N] {
+    [123; N]
+}
+
+fn main() {
+    let arr = my_function::<5>();
+    println!("{:?}",arr);
+}
+```
+
+8、
+```rust
+fn main() {
+    let s: &str = "Hello there!";
+
+    let arr: &[u8] = &[1, 2, 3];
+}
+```
+
+
+9、
+```rust
+use std::fmt::Display;
+fn foobar_1(thing: &dyn Display) {}    
+fn foobar_2(thing: Box<dyn Display>) {} 
+
+fn main() {
+}
+```