Merge branch 'sunface:master' into lifetimes-practice
This commit is contained in:
Lunarix
GitHub
commit
358abc0ff6
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@ -1 +1,2 @@
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book
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book
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.DS_Store
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@ -1,5 +1,10 @@
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# ChangeLog
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### 2022-03-11
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- Add one exercise in [Patterns](https://practice.rs/pattern-match/patterns.html)
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- Add [Result and ?](https://practice.rs/result-panic/result.html)
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### 2022-03-10
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- Add [Type conversions - From/Into](https://practice.rs/type-conversions/from-into.html)
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@ -2,7 +2,7 @@
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This book was designed for easily diving into and get skilled with Rust, and it's very easy to use: All you need to do is to make each exercise compile without ERRORS and Panics !
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> 🎊 Updated on 2022-03-10: Add [Panics](https://practice.rs/result-panic/panic.html)
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> 🎊 Updated on 2022-03-11: Add [Result and ?](https://practice.rs/result-panic/result.html)
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## Reading online
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@ -85,4 +85,17 @@ fn main() {
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}
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}
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}
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```
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6.
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```rust
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fn main() {
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let mut v = String::from("hello,");
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let r = &mut v;
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match r {
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// The type of value is &mut String
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value => value.push_str(" world!")
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}
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}
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```
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@ -0,0 +1,177 @@
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1.
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```rust
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use std::num::ParseIntError;
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fn multiply(n1_str: &str, n2_str: &str) -> Result<i32, ParseIntError> {
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let n1 = n1_str.parse::<i32>();
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let n2 = n2_str.parse::<i32>();
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Ok(n1.unwrap() * n2.unwrap())
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}
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fn main() {
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let result = multiply("10", "2");
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assert_eq!(result, Ok(20));
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let result = multiply("4", "2");
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assert_eq!(result.unwrap(), 8);
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println!("Success!")
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}
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```
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2.
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```rust
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use std::num::ParseIntError;
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// IMPLEMENT multiply with ?
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// DON'T use unwrap here
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fn multiply(n1_str: &str, n2_str: &str) -> Result<i32, ParseIntError> {
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let n1 = n1_str.parse::<i32>()?;
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let n2 = n2_str.parse::<i32>()?;
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Ok(n1 * n2)
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}
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fn main() {
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assert_eq!(multiply("3", "4").unwrap(), 12);
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println!("Success!")
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}
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```
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3.
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```rust
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use std::fs::File;
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use std::io::{self, Read};
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fn read_file1() -> Result<String, io::Error> {
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let f = File::open("hello.txt");
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let mut f = match f {
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Ok(file) => file,
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Err(e) => return Err(e),
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};
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let mut s = String::new();
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match f.read_to_string(&mut s) {
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Ok(_) => Ok(s),
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Err(e) => Err(e),
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}
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}
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fn read_file2() -> Result<String, io::Error> {
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let mut s = String::new();
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File::open("hello.txt")?.read_to_string(&mut s)?;
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Ok(s)
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}
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fn main() {
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assert_eq!(read_file1().unwrap_err().to_string(), read_file2().unwrap_err().to_string());
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println!("Success!")
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}
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```
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4.
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```rust
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use std::num::ParseIntError;
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fn add_two(n_str: &str) -> Result<i32, ParseIntError> {
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n_str.parse::<i32>().map(|num| num +2)
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}
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fn main() {
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assert_eq!(add_two("4").unwrap(), 6);
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println!("Success!")
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}
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```
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```rust
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use std::num::ParseIntError;
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fn add_two(n_str: &str) -> Result<i32, ParseIntError> {
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n_str.parse::<i32>().and_then(|num| Ok(num +2))
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}
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fn main() {
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assert_eq!(add_two("4").unwrap(), 6);
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println!("Success!")
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}
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```
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5.
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```rust
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use std::num::ParseIntError;
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// With the return type rewritten, we use pattern matching without `unwrap()`.
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// But it's so Verbose..
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fn multiply(n1_str: &str, n2_str: &str) -> Result<i32, ParseIntError> {
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match n1_str.parse::<i32>() {
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Ok(n1) => {
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match n2_str.parse::<i32>() {
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Ok(n2) => {
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Ok(n1 * n2)
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},
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Err(e) => Err(e),
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}
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},
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Err(e) => Err(e),
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}
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}
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// Rewriting `multiply` to make it succinct
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// You MUST USING `and_then` and `map` here
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fn multiply1(n1_str: &str, n2_str: &str) -> Result<i32, ParseIntError> {
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// IMPLEMENT...
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n1_str.parse::<i32>().and_then(|n1| {
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n2_str.parse::<i32>().map(|n2| n1 * n2)
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})
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}
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fn print(result: Result<i32, ParseIntError>) {
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match result {
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Ok(n) => println!("n is {}", n),
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Err(e) => println!("Error: {}", e),
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}
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}
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fn main() {
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// This still presents a reasonable answer.
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let twenty = multiply1("10", "2");
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print(twenty);
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// The following now provides a much more helpful error message.
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let tt = multiply("t", "2");
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print(tt);
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println!("Success!")
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}
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```
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6.
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```rust
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use std::num::ParseIntError;
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// Define a generic alias for a `Result` with the error type `ParseIntError`.
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type Res<T> = Result<T, ParseIntError>;
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// Use the above alias to refer to our specific `Result` type.
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fn multiply(first_number_str: &str, second_number_str: &str) -> Res<i32> {
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first_number_str.parse::<i32>().and_then(|first_number| {
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second_number_str.parse::<i32>().map(|second_number| first_number * second_number)
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})
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}
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// Here, the alias again allows us to save some space.
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fn print(result: Res<i32>) {
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match result {
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Ok(n) => println!("n is {}", n),
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Err(e) => println!("Error: {}", e),
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}
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}
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fn main() {
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print(multiply("10", "2"));
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print(multiply("t", "2"));
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}
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```
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@ -38,7 +38,7 @@
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- [Others](type-conversions/others.md)
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- [Result and panic](result-panic/intro.md)
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- [panic!](result-panic/panic.md)
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- [result and ?](result-panic/result.md)
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- [Result and ?](result-panic/result.md)
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- [Crate and module TODO](crate-module/intro.md)
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- [Crate](crate-module/crate.md)
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- [Module](crate-module/module.md)
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@ -101,4 +101,19 @@ fn main() {
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}
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```
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6. 🌟🌟 Using pattern `&mut V` to match a mutable reference needs you to be very careful due to `V` being a value after matching
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```rust,editable
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// FIX the error with least changing
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// DON'T remove any code line
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fn main() {
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let mut v = String::from("hello,");
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let r = &mut v;
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match r {
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&mut value => value.push_str(" world!")
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}
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}
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````
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> You can find the solutions [here](https://github.com/sunface/rust-by-practice)(under the solutions path), but only use it when you need it
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@ -1 +1,212 @@
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# result and ?
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`Result<T>` is an enum to describe possible errors. It has two variants:
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- `Ok(T)`: a value T was found
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- `Err(e)`: An error was found with a value `e`
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In short words, the expected outcome is `Ok`, while the unexpected outcome is `Err`.
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1. 🌟🌟
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```rust,editable
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// FILL in the blanks and FIX the errors
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use std::num::ParseIntError;
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fn multiply(n1_str: &str, n2_str: &str) -> __ {
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let n1 = n1_str.parse::<i32>();
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let n2 = n2_str.parse::<i32>();
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Ok(n1.unwrap() * n2.unwrap())
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}
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fn main() {
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let result = multiply("10", "2");
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assert_eq!(result, __);
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let result = multiply("t", "2");
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assert_eq!(result.__, 8);
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println!("Success!")
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}
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```
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### ?
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`?` is almost exactly equivalent to `unwrap`, but `?` returns instead of panic on `Err`.
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2. 🌟🌟
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```rust,editable
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use std::num::ParseIntError;
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// IMPLEMENT multiply with ?
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// DON'T use unwrap here
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fn multiply(n1_str: &str, n2_str: &str) -> __ {
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}
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fn main() {
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assert_eq!(multiply("3", "4").unwrap(), 12);
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println!("Success!")
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}
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```
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3. 🌟🌟
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```rust,editable
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use std::fs::File;
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use std::io::{self, Read};
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fn read_file1() -> Result<String, io::Error> {
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let f = File::open("hello.txt");
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let mut f = match f {
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Ok(file) => file,
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Err(e) => return Err(e),
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};
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let mut s = String::new();
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match f.read_to_string(&mut s) {
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Ok(_) => Ok(s),
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Err(e) => Err(e),
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}
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}
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// FILL in the blanks with one code line
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// DON'T change any code else
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fn read_file2() -> Result<String, io::Error> {
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let mut s = String::new();
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__;
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Ok(s)
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}
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fn main() {
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assert_eq!(read_file1().unwrap_err().to_string(), read_file2().unwrap_err().to_string());
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println!("Success!")
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}
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```
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### map & and_then
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[map](https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.map) and [and_then](https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.and_then) are two common combinators for `Result<T, E>` (also for `Option<T>`).
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4. 🌟🌟
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```rust,editable
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use std::num::ParseIntError;
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// FILL in the blank in two ways: map, and then
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fn add_two(n_str: &str) -> Result<i32, ParseIntError> {
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n_str.parse::<i32>().__
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}
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fn main() {
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assert_eq!(add_two("4").unwrap(), 6);
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println!("Success!")
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}
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```
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5. 🌟🌟🌟
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```rust,editable
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use std::num::ParseIntError;
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|
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// With the return type rewritten, we use pattern matching without `unwrap()`.
|
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// But it's so Verbose..
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fn multiply(n1_str: &str, n2_str: &str) -> Result<i32, ParseIntError> {
|
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match n1_str.parse::<i32>() {
|
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Ok(n1) => {
|
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match n2_str.parse::<i32>() {
|
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Ok(n2) => {
|
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Ok(n1 * n2)
|
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},
|
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Err(e) => Err(e),
|
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}
|
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},
|
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Err(e) => Err(e),
|
||||
}
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}
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|
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// Rewriting `multiply` to make it succinct
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// You should use BOTH of `and_then` and `map` here.
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fn multiply1(n1_str: &str, n2_str: &str) -> Result<i32, ParseIntError> {
|
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// IMPLEMENT...
|
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}
|
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|
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fn print(result: Result<i32, ParseIntError>) {
|
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match result {
|
||||
Ok(n) => println!("n is {}", n),
|
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Err(e) => println!("Error: {}", e),
|
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}
|
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}
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|
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fn main() {
|
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// This still presents a reasonable answer.
|
||||
let twenty = multiply1("10", "2");
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print(twenty);
|
||||
|
||||
// The following now provides a much more helpful error message.
|
||||
let tt = multiply("t", "2");
|
||||
print(tt);
|
||||
|
||||
println!("Success!")
|
||||
}
|
||||
```
|
||||
|
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### Type alias
|
||||
Using `std::result::Result<T, ParseIntError>` everywhere is verbose and tedious, we can use alias for this purpose.
|
||||
|
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At a module level, creating aliases can be particularly helpful. Errors found in the a specific module often has the same `Err` type, so a single alias can succinctly defined all associated `Results`. This is so useful even the `std` library even supplies one: [`io::Result`](https://doc.rust-lang.org/std/io/type.Result.html).
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||||
|
||||
6. 🌟
|
||||
```rust,editable
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use std::num::ParseIntError;
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||||
|
||||
// FILL in the blank
|
||||
type __;
|
||||
|
||||
// Use the above alias to refer to our specific `Result` type.
|
||||
fn multiply(first_number_str: &str, second_number_str: &str) -> Res<i32> {
|
||||
first_number_str.parse::<i32>().and_then(|first_number| {
|
||||
second_number_str.parse::<i32>().map(|second_number| first_number * second_number)
|
||||
})
|
||||
}
|
||||
|
||||
// Here, the alias again allows us to save some space.
|
||||
fn print(result: Res<i32>) {
|
||||
match result {
|
||||
Ok(n) => println!("n is {}", n),
|
||||
Err(e) => println!("Error: {}", e),
|
||||
}
|
||||
}
|
||||
|
||||
fn main() {
|
||||
print(multiply("10", "2"));
|
||||
print(multiply("t", "2"));
|
||||
|
||||
println!("Success!")
|
||||
}
|
||||
```
|
||||
|
||||
### Using Result in `fn main`
|
||||
Typically `the` main function will look like this:
|
||||
```rust
|
||||
fn main() {
|
||||
println!("Hello World!");
|
||||
}
|
||||
```
|
||||
|
||||
However `main` is also able to have a return type of `Result`. If an error occurs within the `main` function it will return an error code and print a debug representation of the error( Debug trait ).
|
||||
|
||||
The following example shows such a scenario:
|
||||
```rust,editable
|
||||
|
||||
use std::num::ParseIntError;
|
||||
|
||||
fn main() -> Result<(), ParseIntError> {
|
||||
let number_str = "10";
|
||||
let number = match number_str.parse::<i32>() {
|
||||
Ok(number) => number,
|
||||
Err(e) => return Err(e),
|
||||
};
|
||||
println!("{}", number);
|
||||
Ok(())
|
||||
}
|
||||
```
|
||||
|
|
@ -97,4 +97,19 @@ fn main() {
|
|||
}
|
||||
```
|
||||
|
||||
6. 🌟🌟 使用模式 `&mut V` 去匹配一个可变引用时，你需要格外小心，因为匹配出来的 `V` 是一个值，而不是可变引用
|
||||
```rust,editable
|
||||
|
||||
// 修复错误，尽量少地修改代码
|
||||
// 不要移除任何代码行
|
||||
fn main() {
|
||||
let mut v = String::from("hello,");
|
||||
let r = &mut v;
|
||||
|
||||
match r {
|
||||
&mut value => value.push_str(" world!")
|
||||
}
|
||||
}
|
||||
````
|
||||
|
||||
> 你可以在[这里](https://github.com/sunface/rust-by-practice)找到答案(在 solutions 路径下)
|
||||
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Reference in New Issue