add solutions for enum.md

solutions/compound-types/enum.md

@@ -0,0 +1,186 @@
+1.
+```rust
+enum Number {
+    Zero,
+    One,
+    Two,
+}
+
+enum Number1 {
+    Zero = 0,
+    One,
+    Two,
+}
+
+// C-like enum
+enum Number2 {
+    Zero = 0,
+    One = 1,
+    Two = 2,
+}
+
+
+fn main() {
+    // a enum variant can be converted to a integer by `as`
+    assert_eq!(Number::One as u8, Number1::One as u8);
+    assert_eq!(Number1::One as u8, Number2::One as u8);
+} 
+```
+
+2.
+```rust
+enum Message {
+    Quit,
+    Move { x: i32, y: i32 },
+    Write(String),
+    ChangeColor(i32, i32, i32),
+}
+
+fn main() {
+    let msg1 = Message::Move{x: 1, y: 2}; // instantiating with x = 1, y = 2 
+    let msg2 = Message::Write(String::from("hello, world")); // instantiating with "hello, world!"
+} 
+```
+
+3.
+```rust
+enum Message {
+    Quit,
+    Move { x: i32, y: i32 },
+    Write(String),
+    ChangeColor(i32, i32, i32),
+}
+
+fn main() {
+    let msg = Message::Move{x: 1, y: 1};
+
+    if let Message::Move{x: a, y: b} = msg {
+        assert_eq!(a, b);
+    } else {
+        panic!("NEVER LET THIS RUN！");
+    }
+} 
+```
+
+4.
+```rust
+#[derive(Debug)]
+enum Message {
+    Quit,
+    Move { x: i32, y: i32 },
+    Write(String),
+    ChangeColor(i32, i32, i32),
+}
+
+fn main() {
+    let msgs: [Message; 3] = [
+        Message::Quit,
+        Message::Move{x:1, y:3},
+        Message::ChangeColor(255,255,0)
+    ];
+
+    for msg in msgs {
+        show_message(msg)
+    }
+} 
+
+fn show_message(msg: Message) {
+    println!("{:?}", msg);
+}
+```
+
+5.
+```rust
+fn main() {
+    let five = Some(5);
+    let six = plus_one(five);
+    let none = plus_one(None);
+
+    if let Some(n) = six {
+        println!("{}", n);
+        return
+    } 
+    
+    panic!("NEVER LET THIS RUN！");
+} 
+
+fn plus_one(x: Option<i32>) -> Option<i32> {
+    match x {
+        None => None,
+        Some(i) => Some(i + 1),
+    }
+}
+```
+
+6.
+```rust
+use crate::List::*;
+
+enum List {
+    // Cons: Tuple struct that wraps an element and a pointer to the next node
+    Cons(u32, Box<List>),
+    // Nil: A node that signifies the end of the linked list
+    Nil,
+}
+
+// Methods can be attached to an enum
+impl List {
+    // Create an empty list
+    fn new() -> List {
+        // `Nil` has type `List`
+        Nil
+    }
+
+    // Consume a list, and return the same list with a new element at its front
+    fn prepend(self, elem: u32) -> List {
+        // `Cons` also has type List
+        Cons(elem, Box::new(self))
+    }
+
+    // Return the length of the list
+    fn len(&self) -> u32 {
+        // `self` has to be matched, because the behavior of this method
+        // depends on the variant of `self`
+        // `self` has type `&List`, and `*self` has type `List`, matching on a
+        // concrete type `T` is preferred over a match on a reference `&T`
+        // after Rust 2018 you can use self here and tail (with no ref) below as well,
+        // rust will infer &s and ref tail. 
+        // See https://doc.rust-lang.org/edition-guide/rust-2018/ownership-and-lifetimes/default-match-bindings.html
+        match *self {
+            // Can't take ownership of the tail, because `self` is borrowed;
+            // instead take a reference to the tail
+            Cons(_, ref tail) => 1 + tail.len(),
+            // Base Case: An empty list has zero length
+            Nil => 0
+        }
+    }
+
+    // Return representation of the list as a (heap allocated) string
+    fn stringify(&self) -> String {
+        match *self {
+            Cons(head, ref tail) => {
+                // `format!` is similar to `print!`, but returns a heap
+                // allocated string instead of printing to the console
+                format!("{}, {}", head, tail.stringify())
+            },
+            Nil => {
+                format!("Nil")
+            },
+        }
+    }
+}
+
+fn main() {
+    // Create an empty linked list
+    let mut list = List::new();
+
+    // Prepend some elements
+    list = list.prepend(1);
+    list = list.prepend(2);
+    list = list.prepend(3);
+
+    // Show the final state of the list
+    println!("linked list has length: {}", list.len());
+    println!("{}", list.stringify());
+}
+```

src/compound-types/enum.md

@@ -1,5 +1,5 @@
 # Enum
-🌟🌟 Enums can be created with explicit discriminator.
+1. 🌟🌟 Enums can be created with explicit discriminator.
 
 ```rust,editable
 
@@ -31,7 +31,7 @@ fn main() {
 } 
 ```
 
-🌟 each enum variant can hold its own data.
+2. 🌟 each enum variant can hold its own data.
 ```rust,editable
 
 // fill in the blank
@@ -48,10 +48,10 @@ fn main() {
 } 
 ```
 
-🌟🌟 we can get the data which a enum variant is holding by pattern match
+3. 🌟🌟 we can get the data which a enum variant is holding by pattern match
 ```rust,editable
 
-// 仅填空，不要修改其它代码！
+// fill in the blank and fix the error
 enum Message {
     Quit,
     Move { x: i32, y: i32 },
@@ -60,7 +60,7 @@ enum Message {
 }
 
 fn main() {
-    let msg = Message::Move{x: 1, y: 1};
+    let msg = Message::Move{x: 1, y: 2};
 
     if let Message::Move{__} = msg {
         assert_eq!(a, b);
@@ -70,7 +70,7 @@ fn main() {
 } 
 ```
 
-🌟🌟 
+4. 🌟🌟 
 
 ```rust,editable
 
@@ -99,7 +99,7 @@ fn show_message(msg: Message) {
 }
 ```
 
-🌟🌟 As there is no `null` in Rust, we have to use enum  `Option<T>`  to deal the cases when value is absent.
+5. 🌟🌟 As there is no `null` in Rust, we have to use enum  `Option<T>`  to deal the cases when value is absent.
 ```rust,editable
 
 // fill in the blank to make the `println` work.
@@ -125,7 +125,7 @@ fn plus_one(x: Option<i32>) -> Option<i32> {
 ```
 
 
-🌟🌟🌟🌟 implement a `linked-list` via enums.
+6. 🌟🌟🌟🌟 implement a `linked-list` via enums.
 
 ```rust,editable
 

zh-CN/src/compound-types/enum.md

@@ -51,7 +51,7 @@ fn main() {
 🌟🌟 枚举成员中的值可以使用模式匹配来获取
 ```rust,editable
 
-// 仅填空，不要修改其它代码！
+// 仅填空并修复错误
 enum Message {
     Quit,
     Move { x: i32, y: i32 },
@@ -60,7 +60,7 @@ enum Message {
 }
 
 fn main() {
-    let msg = Message::Move{x: 1, y: 1};
+    let msg = Message::Move{x: 1, y: 2};
 
     if let Message::Move{__} = msg {
         assert_eq!(a, b);