add type-conversions/as.md

solutions/type-conversions/as.md

@@ -0,0 +1,88 @@
+1.
+```rust
+fn main() {
+    let decimal = 97.123_f32;
+
+    let integer: u8 = decimal as u8;
+
+    let c1: char = decimal as u8 as char;
+    let c2 = integer as char;
+
+    assert_eq!(integer, 'b' as u8 - 1);
+}
+```
+
+2.
+```rust
+// Suppress all warnings from casts which overflow.
+#![allow(overflowing_literals)]
+
+fn main() {
+    assert_eq!(u8::MAX, 255);
+    let v = 1000 as u8;
+}
+```
+
+3.
+```rust
+fn main() {
+    assert_eq!(1000 as u16, 1000);
+
+    assert_eq!(1000 as u8, 232);
+
+    // For positive numbers, this is the same as the modulus
+    println!("1000 mod 256 is : {}", 1000 % 256);
+
+    assert_eq!(-1_i8 as u8, 255);
+    
+    // Since Rust 1.45, the `as` keyword performs a *saturating cast* 
+    // when casting from float to int. If the floating point value exceeds 
+    // the upper bound or is less than the lower bound, the returned value 
+    // will be equal to the bound crossed.
+    assert_eq!(300.1_f32 as u8, 255);
+    assert_eq!(-100.1_f32 as u8, 0);
+    
+
+    // This behavior incurs a small runtime cost and can be avoided 
+    // with unsafe methods, however the results might overflow and 
+    // return **unsound values**. Use these methods wisely:
+    unsafe {
+        // 300.0 is 44
+        println!("300.0 is {}", 300.0_f32.to_int_unchecked::<u8>());
+        // -100.0 as u8 is 156
+        println!("-100.0 as u8 is {}", (-100.0_f32).to_int_unchecked::<u8>());
+        // nan as u8 is 0
+        println!("nan as u8 is {}", f32::NAN.to_int_unchecked::<u8>());
+    }
+}
+```
+
+4.
+```rust
+fn main() {
+    let mut values: [i32; 2] = [1, 2];
+    let p1: *mut i32 = values.as_mut_ptr();
+    let first_address = p1 as usize; 
+    let second_address = first_address + 4; // 4 == std::mem::size_of::<i32>()
+    let p2 = second_address as *mut i32;
+    unsafe {
+        *p2 += 1;
+    }
+    assert_eq!(values[1], 3);
+
+    println!("Success!")
+}
+```
+
+5.
+```rust
+fn main() {
+    let arr :[u64; 13] = [0; 13];
+    assert_eq!(std::mem::size_of_val(&arr), 8 * 13);
+    let a: *const [u64] = &arr;
+    let b = a as *const [u8];
+    unsafe {
+        assert_eq!(std::mem::size_of_val(&*b), 13)
+    }
+}
+```

src/SUMMARY.md

@@ -32,7 +32,8 @@
   - [String](collections/string.md)
   - [Vector](collections/vector.md)
   - [HashMap](collections/hashmap.md)
-- [Type Conversion todo](type-conversion.md)
+- [Type Conversion](type-conversions/intro.md)
+  - [as](type-conversions/as.md)
 - [Result and panic todo](result-panic/intro.md)
   - [panic!](result-panic/panic.md)
   - [result and ?](result-panic/result.md)

src/collections/hashmap.md

@@ -199,6 +199,8 @@ fn main() {
   m2.insert(v2, v1);
     
   assert_eq!(v2, "hello");
+
+  println!("Success!")
 }
 ```
 

src/type-conversion.md

@@ -1 +0,0 @@
-# Type Conversion

src/type-conversions/as.md

@@ -0,0 +1,103 @@
+# Type Conversions
+Rust provides no implicit type conversion(coercion) between primitive types. But explicit type conversions can be performed using the `as` keyword.
+
+1. 🌟
+```rust,editable
+// FIX the errors and FILL in the blank
+// DON'T remove any code
+fn main() {
+    let decimal = 97.123_f32;
+
+    let integer: __ = decimal as u8;
+
+    let c1: char = decimal as char;
+    let c2 = integer as char;
+
+    assert_eq!(integer, 'b' as u8);
+
+    println!("Success!")
+}
+```
+
+2. 🌟🌟 By default, overflow will cause compile errors, but we can add an global annotation to suppress these errors.
+```rust,editable
+fn main() {
+    assert_eq!(u8::MAX, 255);
+    // the max of `u8` is 255 as shown above.
+    // so the below code will cause an overflow error: literal out of range for `u8`.
+    // PLEASE looking for clues within compile errors to FIX it.
+    // DON'T modify any code in main.
+    let v = 1000 as u8;
+
+    println!("Success!")
+}
+```
+
+3. 🌟🌟  when casting any value to an unsigned type `T`, `T::MAX + 1` is added or subtracted until the value fits into the new type.
+```rust,editable
+fn main() {
+    assert_eq!(1000 as u16, __);
+
+    assert_eq!(1000 as u8, __);
+
+    // For positive numbers, this is the same as the modulus
+    println!("1000 mod 256 is : {}", 1000 % 256);
+
+    assert_eq!(-1_i8 as u8, __);
+    
+    // Since Rust 1.45, the `as` keyword performs a *saturating cast* 
+    // when casting from float to int. If the floating point value exceeds 
+    // the upper bound or is less than the lower bound, the returned value 
+    // will be equal to the bound crossed.
+    assert_eq!(300.1_f32 as u8, __);
+    assert_eq!(-100.1_f32 as u8, __);
+    
+
+    // This behavior incurs a small runtime cost and can be avoided 
+    // with unsafe methods, however the results might overflow and 
+    // return **unsound values**. Use these methods wisely:
+    unsafe {
+        // 300.0 is 44
+        println!("300.0 is {}", 300.0_f32.to_int_unchecked::<u8>());
+        // -100.0 as u8 is 156
+        println!("-100.0 as u8 is {}", (-100.0_f32).to_int_unchecked::<u8>());
+        // nan as u8 is 0
+        println!("nan as u8 is {}", f32::NAN.to_int_unchecked::<u8>());
+    }
+}
+```
+
+4. 🌟🌟🌟 Raw pointer can be converted to memory address (integer) and vice versa
+```rust,editable
+
+// FILL in the blanks
+fn main() {
+    let mut values: [i32; 2] = [1, 2];
+    let p1: *mut i32 = values.as_mut_ptr();
+    let first_address: usize = p1 __; 
+    let second_address = first_address + 4; // 4 == std::mem::size_of::<i32>()
+    let p2: *mut i32 = second_address __; // p2 points to the 2nd element in values
+    unsafe {
+        // add one to the second element
+        __
+    }
+    
+    assert_eq!(values[1], 3);
+
+    println!("Success!")
+}
+```
+
+
+5. 🌟🌟🌟
+```rust,editable
+fn main() {
+    let arr :[u64; 13] = [0; 13];
+    assert_eq!(std::mem::size_of_val(&arr), 8 * 13);
+    let a: *const [u64] = &arr;
+    let b = a as *const [u8];
+    unsafe {
+        assert_eq!(std::mem::size_of_val(&*b), __)
+    }
+}
+```

src/type-conversions/intro.md

@@ -0,0 +1,2 @@
+# Type conversions
+There are several ways we can use to perform type conversions, such as `as`, `From/Intro`, `TryFrom/TryInto`, `transmute` etc.

zh-CN/src/collections/String.md

@@ -150,7 +150,7 @@ fn main() {
 
 存储在栈上的智能指针结构体由三部分组成：一个指针只指向堆上的字节数组，已使用的长度以及已分配的容量 capacity (已使用的长度小于等于已分配的容量，当容量不够时，会重新分配内存空间)。
 
-1. 🌟🌟 如果 String 的当前容量足够，那么添加字符将不会导致新的内存分配
+6. 🌟🌟 如果 String 的当前容量足够，那么添加字符将不会导致新的内存分配
 ```rust,editable
 
 // 修改下面的代码以打印如下内容: 

zh-CN/src/collections/hashmap.md

@@ -105,7 +105,7 @@ fn random_stat_buff() -> u8 {
 如果一个集合类型的所有字段都实现了 `Eq` 和 `Hash`,那该集合类型会自动实现 `Eq` 和 `Hash`。例如 `Vect<T>` 要实现 `Hash`，那么首先需要 `T` 实现 `Hash`。
 
 
-1. 🌟🌟
+4. 🌟🌟
 ```rust,editable
 
 // 修复错误
@@ -171,7 +171,7 @@ fn main() {
 对于实现了 `Copy` 特征的类型，例如 `i32`，那类型的值会被拷贝到 `HashMap` 中。而对于有所有权的类型，例如 `String`，它们的值的所有权将被转移到 `HashMap` 中。
 
 
-1. 🌟🌟
+5. 🌟🌟
 ```rust,editable
 // 修复错误，尽可能少的去修改代码
 // 不要移除任何代码行！
@@ -188,6 +188,8 @@ fn main() {
   m2.insert(v2, v1);
     
   assert_eq!(v2, "hello");
+
+   println!("Success!")
 }
 ```