type-conversions/from-into #212

2022-04-15T12:02:00Z

giscus[bot]
bot Apr 15, 2022

type-conversions/from-into

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https://zh.practice.rs/type-conversions/from-into.html

zmh1994 · 2022-04-15T12:02:01Z

zmh1994
Apr 15, 2022 — with giscus

这节练习题对应的讲解在哪儿啊？我怎么没找到

2 replies

zhaojuncw Jun 6, 2022 — with giscus

书上好像没有对应的章节，只能翻标准库了

tjw123hh Aug 9, 2023 — with giscus

https://course.rs/advance/into-types/converse.html

jingth · 2022-10-04T04:01:34Z

jingth
Oct 4, 2022 — with giscus

/*
fn main() {
// impl From for i32
let i1:i32 = false.into();
let i2:i32 = i32::from(false);
assert_eq!(i1, i2);
assert_eq!(i1, 0);

// 使用两种方式修复错误
// 1. 哪个类型实现 From 特征 : impl From for ? , 你可以查看一下之前提到的文档，来找到合适的类型
// 2. 上一章节中介绍过的某个关键字

let i3: u32 = 'a'.into();

// 使用两种方法来解决错误
//let s: String = 'a'.into();
let s: String = String::from('a');

println!("Success!")
}
*/

/*
// From 被包含在 std::prelude 中，因此我们没必要手动将其引入到当前作用域来
// use std::convert::From;

#[derive(Debug)]
struct Number {
value: i32,
}

impl From for Number {
// 实现 `from' 方法
fn from(x: i32) -> Self {
Number{value: x}
}
}

// 填空
fn main() {
let num = Number{value: 30};
assert_eq!(num.value, 30);

let num: Number = 30.into();
assert_eq!(num.value, 30);

println!("Success!")

}
*/

/*
use std::fs;
use std::io;
use std::num;

enum CliError {
IoError(io::Error),
ParseError(num::ParseIntError),
}

impl Fromio::Error for CliError {
// 实现 from 方法
fn from(e: io::Error) -> Self {
println!("这是一个IO错误");
CliError::IoError(e)
}
}

impl Fromnum::ParseIntError for CliError {
// 实现 from 方法
fn from(e: num::ParseIntError) -> Self {
println!("这是一个ParseIntError错误");
CliError::ParseError(e)
}
}

fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
// ? 自动将 io::Error 转换成 CliError
let contents = fs::read_to_string(&file_name)?;
// num::ParseIntError -> CliError
let num: i32 = contents.trim().parse()?;
Ok(num)
}

fn main() {
println!("Success!")
}
*/

/*
// TryFrom 和 TryInto 也被包含在 std::prelude 中, 因此以下引入是没必要的
// use std::convert::TryInto;

fn main() {
let n: i16 = 256;

// Into 特征拥有一个方法`into`,
// 因此 TryInto 有一个方法是 ?
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!")

}
*/

#[derive(Debug, PartialEq)]
struct EvenNum(i32);

impl TryFrom for EvenNum {
type Error = ();

// 实现 `try_from`
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(()));

// 填空
let result: Result<EvenNum, ()> = 8i32.try_into();
assert_eq!(result, Ok(EvenNum(8)));
let result: Result<EvenNum, ()> = 5i32.try_into();
assert_eq!(result, Err(()));

println!("Success!")

}

0 replies

ADkun · 2022-10-09T08:11:44Z

ADkun
Oct 9, 2022 — with giscus

第1题

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);

    // 使用两种方式修复错误
    // 1. 哪个类型实现 From 特征 : impl From<char> for ? , 你可以查看一下之前提到的文档，来找到合适的类型
    // 2. 上一章节中介绍过的某个关键字
    let i3: i32 = 'a' as i32;
    unsafe {
        let i3: i32 = std::mem::transmute_copy::<char, i32>(&'a');
    }

    // 使用两种方法来解决错误
    let s: String = 'a'.into();
    let s: String = String::from('a');

    println!("Success!")
}

第2题

// From 被包含在 `std::prelude` 中，因此我们没必要手动将其引入到当前作用域来
// use std::convert::From;

#[derive(Debug)]
struct Number {
    value: i32,
}

impl From<i32> for Number {
    // 实现 `from` 方法
    fn from(value: i32) -> Self {
        Self {
            value
        }
    }
}

// 填空
fn main() {
    let num = Number{ value: 30 };
    assert_eq!(num.value, 30);

    let num: Number = 30_i32.into();
    assert_eq!(num.value, 30);

    println!("Success!")
}

第3题

use std::fs;
use std::io;
use std::num;

#[derive(Debug)]
enum CliError {
    IoError(io::Error),
    ParseError(num::ParseIntError),
}

impl From<io::Error> for CliError {
    // 实现 from 方法
    fn from(src: io::Error) -> Self {
        Self::IoError(src)
    }
}

impl From<num::ParseIntError> for CliError {
    // 实现 from 方法
    fn from(src: num::ParseIntError) -> Self {
        Self::ParseError(src)
    }
}

fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
    // ? 自动将 io::Error 转换成 CliError
    let contents = fs::read_to_string(&file_name)?;
    // num::ParseIntError -> CliError
    let num: i32 = contents.trim().parse()?;
    Ok(num)
}

fn main() {
    match open_and_parse_file("abc") {
        Ok(num) => println!("ok, {}", num),
        Err(e) => println!("err: {:?}", e),
    }
    println!("Success!")
}

第4题

// TryFrom 和 TryInto 也被包含在 `std::prelude` 中, 因此以下引入是没必要的
// use std::convert::TryInto;

fn main() {
    let n: i16 = 256;

    // Into 特征拥有一个方法`into`,
    // 因此 TryInto 有一个方法是 ?
    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!")
}

第5题

#[derive(Debug, PartialEq)]
struct EvenNum(i32);

impl TryFrom<i32> for EvenNum {
    type Error = ();

    // 实现 `try_from`
    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(()));

    // 填空
    let result: Result<EvenNum, ()> = 8i32.try_into();
    assert_eq!(result, Ok(EvenNum(8)));
    let result: Result<EvenNum, ()> = 5i32.try_into();
    assert_eq!(result, Err(()));

    println!("Success!")
}

0 replies

ZLD1819858 · 2022-11-09T17:15:43Z

ZLD1819858
Nov 9, 2022 — with giscus

原来into()方法和From特征有这样的关系啊！顿悟了！前面老纳闷into()方法怎么转啥都行...就是需要显式指定类型

0 replies

Bruce012356 · 2023-01-09T07:08:58Z

Bruce012356
Jan 9, 2023 — with giscus

mark

1 reply

runzhi214 Jul 26, 2023 — with giscus

第四题

try_into()
另外，256转u8明显超限了，所以报错 assert_eq!(n, 0);

chenhai998 · 2023-08-06T14:28:54Z

chenhai998
Aug 6, 2023 — with giscus

done

0 replies

iamtaojin · 2023-12-12T12:20:44Z

iamtaojin
Dec 12, 2023 — with giscus

第一题

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);

    // 使用两种方式修复错误
    // 1. 哪个类型实现 From 特征 : impl From<char> for ? , 你可以查看一下之前提到的文档，来找到合适的类型
    // 2. 上一章节中介绍过的某个关键字
    let i3: i32 = 'a' as i32;
    unsafe {
        let i3: i32 = std::mem::transmute_copy::<char, i32>(&'a');
    }

    // 使用两种方法来解决错误
    let s: String = 'a'.into();
    let s: String = String::from('a');

    println!("Success!")
}

第二题

// From 被包含在 `std::prelude` 中，因此我们没必要手动将其引入到当前作用域来
// use std::convert::From;

#[derive(Debug)]
struct Number {
    value: i32,
}

impl From<i32> for Number {
    fn from(v: i32) -> Number{
        Number{
            value: v,
        }
    }
}

// 填空
fn main() {
    let num = Number::from(30);
    assert_eq!(num.value, 30);

    let num: Number = Number{value:30};
    assert_eq!(num.value, 30);

    println!("Success!")
}

第三题

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(err: io::Error) -> Self{
        CliError::IoError(err)
    }
}

impl From<num::ParseIntError> for CliError {
    fn from(err: num::ParseIntError) -> CliError{
        CliError::ParseError(err)
    }
}

fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
    // ? 自动将 io::Error 转换成 CliError
    let contents = fs::read_to_string(&file_name)?;
    // num::ParseIntError -> CliError
    let num: i32 = contents.trim().parse()?;
    Ok(num)
}

fn main() {
    println!("Success!")
}

第四题

// TryFrom 和 TryInto 也被包含在 `std::prelude` 中, 因此以下引入是没必要的
// use std::convert::TryInto;

fn main() {
    let n: i16 = 256;

    // Into 特征拥有一个方法`into`,
    // 因此 TryInto 有一个方法是 ?
    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!")
}

第五题

#[derive(Debug, PartialEq)]
struct EvenNum(i32);

impl TryFrom<i32> for EvenNum {
    type Error = ();

    // 实现 `try_from`
    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(()));

    // 填空
    let result: Result<EvenNum, ()> = 8i32.try_into();
    assert_eq!(result, Ok(EvenNum(8)));
    let result: Result<EvenNum, ()> = 5i32.try_into();
    assert_eq!(result, Err(()));

    println!("Success!")
}

0 replies

TDAkory · 2024-07-21T10:23:55Z

TDAkory
Jul 21, 2024 — with giscus

mark finished

0 replies

Lianghua007 · 2024-08-03T07:08:42Z

Lianghua007
Aug 3, 2024 — with giscus

第一题

#[warn(unused_variables)]
fn main() {
    // impl From<bool> for i32
    let i1: i32 = false.into();     // i1 = 0
    let i2: i32 = i32::from(false); // i2 = 0
    assert_eq!(i1, i2);
    assert_eq!(i1, 0);

    // 使用两种方式修复错误
    // 1. 哪个类型实现 From 特征 : impl From<char> for u32/u64/u128/String , 你可以查看一下之前提到的文档，来找到合适的类型
    // 2. 上一章节中介绍过的某个关键字
    let i3: i32 = u32::from('a') as i32;   // 使用内置From实现char->u32 

    // 使用两种方法来解决错误
    // let s: String = String::from('a');
    let s: String = 'a'.into();

    println!("Success!")
}

第二题

// From 被包含在 `std::prelude` 中，因此我们没必要手动将其引入到当前作用域来
// use std::convert::From;

#[derive(Debug)]
struct Number {
    value: i32,
}

impl From<i32> for Number {     // 为Number实现From
    fn from(num: i32) -> Self { // 返回一个Number/Self类型
        Self {  // 定义Number，并进行值绑定
            value: num
        }
    }
}

// 填空
fn main() {
    let num = Number::from(30);
    assert_eq!(num.value, 30);

    let num: Number = 30.into();
    assert_eq!(num.value, 30);

    println!("Success!")
}

第三题

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(e: io::Error) -> Self{ 
        CliError::IoError(e)
    }
}

impl From<num::ParseIntError> for CliError {
    fn from(e: num::ParseIntError) -> Self {
        CliError::ParseError(e)
    }
}

fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
    // ? 自动将 io::Error 转换成 CliError
    let contents = fs::read_to_string(&file_name)?;

    // num::ParseIntError -> CliError
    let num: i32 = contents.trim().parse()?;
    Ok(num)
}

fn main() {
    println!("Success!")
}

第四题

// TryFrom 和 TryInto 也被包含在 `std::prelude` 中, 因此以下引入是没必要的
// use std::convert::TryInto;

fn main() {
    let n: i16 = 256;

    // Into 特征拥有一个方法`into`,
    // 因此 TryInto 有一个方法是 'try_into'
    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!("n = {}", n);   
    println!("Success!")
}

第五题

#[derive(Debug, PartialEq)]
struct EvenNum(i32);

impl TryFrom<i32> for EvenNum {
    type Error = ();    // 关联类型

    // 实现 `try_from`
    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(()));

    // 填空
    let result: Result<EvenNum, ()> = 8i32.try_into();
    assert_eq!(result, Ok(EvenNum(8)));
    let result: Result<EvenNum, ()> = 5i32.try_into();
    assert_eq!(result, Err(()));

    println!("Success!")
}

0 replies

bansal-harsh-2504 · 2024-12-19T06:52:31Z

bansal-harsh-2504
Dec 19, 2024 — with giscus

Day 10
Done ✅

0 replies

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type-conversions/from-into #212

giscus[bot] bot Apr 15, 2022

type-conversions/from-into

Replies: 10 comments · 3 replies

zmh1994 Apr 15, 2022 — with giscus

zhaojuncw Jun 6, 2022 — with giscus

tjw123hh Aug 9, 2023 — with giscus

jingth Oct 4, 2022 — with giscus

ADkun Oct 9, 2022 — with giscus

第1题

第2题

第3题

第4题

第5题

ZLD1819858 Nov 9, 2022 — with giscus

Bruce012356 Jan 9, 2023 — with giscus

runzhi214 Jul 26, 2023 — with giscus

第四题

chenhai998 Aug 6, 2023 — with giscus

iamtaojin Dec 12, 2023 — with giscus

第一题

第二题

第三题

第四题

第五题

TDAkory Jul 21, 2024 — with giscus

Lianghua007 Aug 3, 2024 — with giscus

第一题

第二题

第三题

第四题

第五题

bansal-harsh-2504 Dec 19, 2024 — with giscus

giscus[bot]
bot Apr 15, 2022

Replies: 10 comments 3 replies

zmh1994
Apr 15, 2022 — with giscus

jingth
Oct 4, 2022 — with giscus

ADkun
Oct 9, 2022 — with giscus

ZLD1819858
Nov 9, 2022 — with giscus

Bruce012356
Jan 9, 2023 — with giscus

chenhai998
Aug 6, 2023 — with giscus

iamtaojin
Dec 12, 2023 — with giscus

TDAkory
Jul 21, 2024 — with giscus

Lianghua007
Aug 3, 2024 — with giscus

bansal-harsh-2504
Dec 19, 2024 — with giscus