Merge pull request #287 from Tanish-Eagle/edit

Edited type-conversionEdit
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Sunface 2022-08-08 10:09:21 +08:00 committed by GitHub
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3 changed files with 26 additions and 26 deletions

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@ -15,7 +15,7 @@ fn main() {
assert_eq!(integer, 'b' as u8);
println!("Success!")
println!("Success!");
}
```
@ -23,17 +23,17 @@ fn main() {
```rust,editable
fn main() {
assert_eq!(u8::MAX, 255);
// the max of `u8` is 255 as shown above.
// 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!")
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.
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, __);
@ -67,7 +67,7 @@ fn main() {
}
```
4. 🌟🌟🌟 Raw pointer can be converted to memory address (integer) and vice versa
4. 🌟🌟🌟 Raw pointers can be converted to memory address (integer) and vice versa.
```rust,editable
// FILL in the blanks
@ -78,13 +78,13 @@ fn main() {
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
// Add one to the second element
__
}
assert_eq!(values[1], 3);
println!("Success!")
println!("Success!");
}
```
@ -100,6 +100,6 @@ fn main() {
assert_eq!(std::mem::size_of_val(&*b), __)
}
println!("Success!")
println!("Success!");
}
```

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@ -8,7 +8,7 @@ The `Into` trait is simply the reciprocal of the `From` trait. That is, if you h
Using the `Into` trait will typically require the type annotations as the compiler is unable to determine this most of the time.
For example we can easily convert `&str` into `String` :
For example, we can easily convert `&str` into `String` :
```rust
fn main() {
let my_str = "hello";
@ -16,12 +16,12 @@ fn main() {
// three conversions below all depends on the fact: String implements From<&str>:
let string1 = String::from(my_str);
let string2 = my_str.to_string();
// explict type annotation is required here
// Explicit type annotation is required here
let string3: String = my_str.into();
}
```
because the standard library has already implemented this for us : `impl From<&'_ str> for String` .
Because the standard library has already implemented this for us : `impl From<&'_ str> for String` .
Some implementations of `From` trait can be found [here](https://doc.rust-lang.org/stable/std/convert/trait.From.html#implementors).
@ -43,7 +43,7 @@ fn main() {
// FIX the error in two ways
let s: String = 'a' as String;
println!("Success!")
println!("Success!");
}
```
@ -71,7 +71,7 @@ fn main() {
let num: Number = __;
assert_eq!(num.value, 30);
println!("Success!")
println!("Success!");
}
```
@ -104,7 +104,7 @@ fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
}
fn main() {
println!("Success!")
println!("Success!");
}
```
@ -134,7 +134,7 @@ fn main() {
assert_eq!(n, __);
println!("Success!")
println!("Success!");
}
```
@ -166,6 +166,6 @@ fn main() {
let result: Result<EvenNum, ()> = 5i32.try_into();
assert_eq!(result, __);
println!("Success!")
println!("Success!");
}
```

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@ -1,7 +1,7 @@
# Others
### Convert any type to String
To convert any type to `String`, you can simply the `ToString` trait for that type. Rather than doing that directly, you should implement the `fmt::Display` trait which will automatically provides `ToString` and also allows you to print the type with `println!`.
To convert any type to `String`, you can simply use the `ToString` trait for that type. Rather than doing that directly, you should implement the `fmt::Display` trait which will automatically provides `ToString` and also allows you to print the type with `println!`.
1. 🌟🌟
```rust,editable
@ -22,14 +22,14 @@ fn main() {
assert_eq!(origin.__, "The point is (0, 0)");
assert_eq!(format!(__), "The point is (0, 0)");
println!("Success!")
println!("Success!");
}
```
### Parse a String
2. 🌟🌟🌟 We can use `parse` method to convert a `String` into a `i32` number, this is becuase `FromStr` is implemented for `i32` type in standard library: `impl FromStr for i32`
2. 🌟🌟🌟 We can use `parse` method to convert a `String` into a `i32` number, this is because `FromStr` is implemented for `i32` type in standard library: `impl FromStr for i32`
```rust,editable
// To use `from_str` method, you needs to introduce this trait into the current scope.
// To use `from_str` method, you need to introduce this trait into the current scope.
use std::str::FromStr;
fn main() {
let parsed: i32 = "5".__.unwrap();
@ -38,7 +38,7 @@ fn main() {
let sum = parsed + turbo_parsed + from_str;
assert_eq!(sum, 35);
println!("Success!")
println!("Success!");
}
```
@ -74,14 +74,14 @@ fn main() {
let p = __;
assert_eq!(p.unwrap(), Point{ x: 3, y: 4} );
println!("Success!")
println!("Success!");
}
```
### Deref
You can find all the examples and exercises of the `Deref` trait [here](https://practice.rs/smart-pointers/deref.html).
### transmute
### Transmute
`std::mem::transmute` is a **unsafe function** can be used to reinterprets the bits of a value of one type as another type. Both of the original and the result types must have the same size and neither of them can be invalid.
`transmute` is semantically equivalent to a bitwise move of one type into another. It copies the bits from the source value into the destination value, then forgets the original, seems equivalent to C's `memcpy` under the hood.
@ -126,9 +126,9 @@ fn main() {
let num = unsafe { std::mem::transmute::<[u8; 4], u32>(raw_bytes) };
// use `u32::from_ne_bytes` instead
// Use `u32::from_ne_bytes` instead
let num = u32::from_ne_bytes(raw_bytes);
// or use `u32::from_le_bytes` or `u32::from_be_bytes` to specify the endianness
// Or use `u32::from_le_bytes` or `u32::from_be_bytes` to specify the endianness
let num = u32::from_le_bytes(raw_bytes);
assert_eq!(num, 0x12345678);
let num = u32::from_be_bytes(raw_bytes);
@ -150,7 +150,7 @@ fn main() {
let val_casts = unsafe { &mut *(ptr as *mut i32 as *mut u32) };
/*Turning an &str into a &[u8]: */
// this is not a good way to do this.
// This is not a good way to do this.
let slice = unsafe { std::mem::transmute::<&str, &[u8]>("Rust") };
assert_eq!(slice, &[82, 117, 115, 116]);