144 lines
2.5 KiB
Markdown
144 lines
2.5 KiB
Markdown
1.
|
|
|
|
```rust
|
|
fn main() {
|
|
// impl From<bool> for i32
|
|
let i1:i32 = false.into();
|
|
let i2:i32 = i32::from(false);
|
|
assert_eq!(i1, i2);
|
|
assert_eq!(i1, 0);
|
|
|
|
let i3: u32 = 'a'.into();
|
|
|
|
let s: String = 'a'.into();
|
|
}
|
|
```
|
|
|
|
```rust
|
|
fn main() {
|
|
// impl From<bool> for i32
|
|
let i1:i32 = false.into();
|
|
let i2:i32 = i32::from(false);
|
|
assert_eq!(i1, i2);
|
|
assert_eq!(i1, 0);
|
|
|
|
let i3: u32 = 'a' as u32 ;
|
|
|
|
let s: String = String::from('a');
|
|
}
|
|
```
|
|
|
|
2.
|
|
|
|
```rust
|
|
// From is now included in `std::prelude`, so there is no need to introduce it into the current scope
|
|
// use std::convert::From;
|
|
|
|
#[derive(Debug)]
|
|
struct Number {
|
|
value: i32,
|
|
}
|
|
|
|
impl From<i32> for Number {
|
|
// IMPLEMENT `from` method
|
|
fn from(item: i32) -> Self {
|
|
Number { value: item }
|
|
}
|
|
}
|
|
|
|
fn main() {
|
|
let num = Number::from(30);
|
|
assert_eq!(num.value, 30);
|
|
|
|
let num: Number = 30.into();
|
|
assert_eq!(num.value, 30);
|
|
|
|
println!("Success!")
|
|
}
|
|
```
|
|
|
|
3.
|
|
|
|
```rust
|
|
use std::fs;
|
|
use std::io;
|
|
use std::num;
|
|
|
|
enum CliError {
|
|
IoError(io::Error),
|
|
ParseError(num::ParseIntError),
|
|
}
|
|
|
|
impl From<io::Error> for CliError {
|
|
fn from(error: io::Error) -> Self {
|
|
CliError::IoError(error)
|
|
}
|
|
}
|
|
|
|
impl From<num::ParseIntError> for CliError {
|
|
fn from(error: num::ParseIntError) -> Self {
|
|
CliError::ParseError(error)
|
|
}
|
|
}
|
|
|
|
fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
|
|
// ? automatically converts io::Error to CliError
|
|
let contents = fs::read_to_string(&file_name)?;
|
|
// num::ParseIntError -> CliError
|
|
let num: i32 = contents.trim().parse()?;
|
|
Ok(num)
|
|
}
|
|
|
|
fn main() {
|
|
println!("Success!")
|
|
}
|
|
```
|
|
|
|
4.
|
|
|
|
```rust
|
|
fn main() {
|
|
let n: i16 = 256;
|
|
|
|
let n: u8 = match n.try_into() {
|
|
Ok(n) => n,
|
|
Err(e) => {
|
|
println!("there is an error when converting: {:?}, but we catch it", e.to_string());
|
|
0
|
|
}
|
|
};
|
|
|
|
assert_eq!(n, 0);
|
|
|
|
println!("Success!")
|
|
}
|
|
```
|
|
|
|
5.
|
|
|
|
```rust,editable
|
|
#[derive(Debug, PartialEq)]
|
|
struct EvenNum(i32);
|
|
|
|
impl TryFrom<i32> for EvenNum {
|
|
type Error = ();
|
|
|
|
fn try_from(value: i32) -> Result<Self, Self::Error> {
|
|
if value % 2 == 0 {
|
|
Ok(EvenNum(value))
|
|
} else {
|
|
Err(())
|
|
}
|
|
}
|
|
}
|
|
|
|
fn main() {
|
|
assert_eq!(EvenNum::try_from(8), Ok(EvenNum(8)));
|
|
assert_eq!(EvenNum::try_from(5), Err(()));
|
|
|
|
let result: Result<EvenNum, ()> = 8i32.try_into();
|
|
assert_eq!(result, Ok(EvenNum(8)));
|
|
let result: Result<EvenNum, ()> = 5i32.try_into();
|
|
assert_eq!(result, Err(()));
|
|
}
|
|
``` |