Rust vs Go:常用语法对比(八)

题目来自 Golang vs. Rust: Which Programming Language To Choose in 2023?

141. <font color="0c0a3e">Iterate in sequence over two lists</font>

Iterate in sequence over the elements of the list items1 then items2. For each iteration print the element.

*依次迭代两个列表
依次迭代列表项1和项2的元素。每次迭代打印元素。*

package main

import (
    "fmt"
)

func main() {
    items1 := []string{"a", "b", "c"}
    items2 := []string{"A", "B", "C"}

    for _, v := range items1 {
        fmt.Println(v)
    }
    for _, v := range items2 {
        fmt.Println(v)
    }
}

a
b
c
A
B
C

---

fn main() {
    let item1 = vec!["1", "2", "3"];
    let item2 = vec!["a", "b", "c"];
    for i in item1.iter().chain(item2.iter()) {
        print!("{} ", i);
    }
}

1 2 3 a b c

142. <font color="0c0a3e">Hexadecimal digits of an integer</font>

Assign to string s the hexadecimal representation (base 16) of integer x.
E.g. 999 -> "3e7"

将整数x的十六进制表示(16进制)赋给字符串s。

package main

import "fmt"
import "strconv"

func main() {
    x := int64(999)
    s := strconv.FormatInt(x, 16)

    fmt.Println(s)
}

3e7

or

package main

import (
    "fmt"
    "math/big"
)

func main() {
    x := big.NewInt(999)
    s := fmt.Sprintf("%x", x)

    fmt.Println(s)
}

3e7

---

fn main() {
    let x = 999;

    let s = format!("{:X}", x);
    println!("{}", s);

    let s = format!("{:x}", x);
    println!("{}", s);
}

**{:X} produces uppercase hex.
{:x} produces lowercase hex.**

3E7
3e7

143. <font color="0c0a3e">Iterate alternatively over two lists</font>

Iterate alternatively over the elements of the list items1 and items2. For each iteration, print the element.
Explain what happens if items1 and items2 have different size.

交替迭代两个列表

package main

import (
    "fmt"
)

func main() {
    items1 := []string{"a", "b"}
    items2 := []string{"A", "B", "C"}

    for i := 0; i < len(items1) || i < len(items2); i++ {
        if i < len(items1) {
            fmt.Println(items1[i])
        }
        if i < len(items2) {
            fmt.Println(items2[i])
        }
    }
}

a
A
b
B
C

---

extern crate itertools;
use itertools::izip;

fn main() {
    let items1 = [5, 15, 25];
    let items2 = [10, 20, 30];

    for pair in izip!(&items1, &items2) {
        println!("{}", pair.0);
        println!("{}", pair.1);
    }
}

5
10
15
20
25
30

144. <font color="0c0a3e">Check if file exists</font>

Set boolean b to true if file at path fp exists on filesystem; false otherwise.
Beware that you should never do this and then in the next instruction assume the result is still valid, this is a race condition on any multitasking OS.

检查文件是否存在

package main

import (
    "fmt"
    "io/ioutil"
    "os"
)

func main() {
    fp := "foo.txt"
    _, err := os.Stat(fp)
    b := !os.IsNotExist(err)
    fmt.Println(fp, "exists:", b)

    fp = "bar.txt"
    _, err = os.Stat(fp)
    b = !os.IsNotExist(err)
    fmt.Println(fp, "exists:", b)
}

func init() {
    ioutil.WriteFile("foo.txt", []byte(`abc`), 0644)
}

There's no specific existence check func in standard library, so we have to inspect an error return value.

foo.txt exists: true
bar.txt exists: false

---

fn main() {
    let fp = "/etc/hosts";
    let b = std::path::Path::new(fp).exists();
    println!("{}: {}", fp, b);

    let fp = "/etc/kittens";
    let b = std::path::Path::new(fp).exists();
    println!("{}: {}", fp, b);
}

/etc/hosts: true
/etc/kittens: false

145. <font color="0c0a3e">Print log line with datetime</font>

Print message msg, prepended by current date and time.
Explain what behavior is idiomatic: to stdout or stderr, and what the date format is.

打印带时间的日志

package main

import "log"

func main() {
    msg := "Hello, playground"
    log.Println(msg)

    // The date is fixed in the past in the Playground, never mind.
}

// See http://www.programming-idioms.org/idiom/145/print-log-line-with-date/1815/go

2009/11/10 23:00:00 Hello, playground

---

fn main() {
    let msg = "Hello";
    eprintln!("[{}] {}", humantime::format_rfc3339_seconds(std::time::SystemTime::now()), msg);
}

[2021-07-17T07:14:03Z] Hello

146. <font color="0c0a3e">Convert string to floating point number</font>

Extract floating point value f from its string representation s

字符串转换为浮点型

package main

import (
    "fmt"
    "strconv"
)

func main() {
    s := "3.1415926535"

    f, err := strconv.ParseFloat(s, 64)
    fmt.Printf("%T, %v, err=%v\n", f, f, err)
}

//
// http://www.programming-idioms.org/idiom/146/convert-string-to-floating-point-number/1819/go
//

float64, 3.1415926535, err=<nil>

---

fn main() {
    let s = "3.14159265359";
    let f = s.parse::<f32>().unwrap();
    
    println!("{}² = {}" , f, f * f);
}

3.1415927² = 9.869605

or

fn main() {
    let s = "3.14159265359";
    let f: f32 = s.parse().unwrap();

    println!("{}² = {}", f, f * f);
}

3.1415927² = 9.869605

147. <font color="0c0a3e">Remove all non-ASCII characters</font>

Create string t from string s, keeping only ASCII characters

移除所有的非ASCII字符

package main

import (
    "fmt"
    "regexp"
)

func main() {
    s := "dæmi : пример : příklad : thí dụ"

    re := regexp.MustCompile("[[:^ascii:]]")
    t := re.ReplaceAllLiteralString(s, "")

    fmt.Println(t)
}

dmi : : pklad : th d

or

package main

import (
    "fmt"
    "strings"
    "unicode"
)

func main() {
    s := "5#∑∂ƒ∞645eyfu"
    t := strings.Map(func(r rune) rune {
        if r > unicode.MaxASCII {
            return -1
        }
        return r
    }, s)
    fmt.Println(t)
}

5#645eyfu

---

fn main() {
    println!("{}", "do👍ot".replace(|c: char| !c.is_ascii(), ""))
}

doot

or

fn main() {
    println!("{}", "do👍ot".replace(|c: char| !c.is_ascii(), ""))
}

doot

148. <font color="0c0a3e">Read list of integers from stdin</font>

Read a list of integer numbers from the standard input, until EOF.

从stdin(标准输入)中读取整数列表

package main

import (
    "bufio"
    "fmt"
    "log"
    "strconv"
    "strings"
)

func main() {
    var ints []int
    s := bufio.NewScanner(osStdin)
    s.Split(bufio.ScanWords)
    for s.Scan() {
        i, err := strconv.Atoi(s.Text())
        if err == nil {
            ints = append(ints, i)
        }
    }
    if err := s.Err(); err != nil {
        log.Fatal(err)
    }
    fmt.Println(ints)
}

// osStdin simulates os.Stdin
var osStdin = strings.NewReader(`
11
22
33  `)

[11 22 33]

---

use std::{
    io::{self, Read},
    str::FromStr,
};

// dummy io::stdin
fn io_stdin() -> impl Read {
    "123
456
789"
    .as_bytes()
}

fn main() -> io::Result<()> {
    let mut string = String::new();
    io_stdin().read_to_string(&mut string)?;
    let result = string
        .lines()
        .map(i32::from_str)
        .collect::<Result<Vec<_>, _>>();
    println!("{:#?}", result);
    Ok(())
}

Ok(
    [
        123,
        456,
        789,
    ],
)

150. <font color="0c0a3e">Remove trailing slash</font>

Remove last character from string p, if this character is a slash /.

去除末尾的 /

package main

import (
    "fmt"
    "strings"
)

func main() {
    p := "/usr/bin/"

    p = strings.TrimSuffix(p, "/")

    fmt.Println(p)
}

/usr/bin

---

fn main() {
    let mut p = String::from("Dddd/");
    if p.ends_with('/') {
        p.pop();
    }
    println!("{}", p);
}

Dddd

151. <font color="0c0a3e">Remove string trailing path separator</font>

Remove last character from string p, if this character is the file path separator of current platform.
Note that this also transforms unix root path "/" into the empty string!

删除字符串尾部路径分隔符

package main

import (
    "fmt"
    "io/ioutil"
    "os"
    "strings"
)

func main() {
    p := somePath()
    fmt.Println(p)

    sep := fmt.Sprintf("%c", os.PathSeparator)
    p = strings.TrimSuffix(p, sep)

    fmt.Println(p)
}

func somePath() string {
    dir, err := ioutil.TempDir("", "")
    if err != nil {
        panic(err)
    }
    p := fmt.Sprintf("%s%c%s%c", dir, os.PathSeparator, "foobar", os.PathSeparator)
    return p
}

/tmp/067319278/foobar/
/tmp/067319278/foobar

or

package main

import (
    "fmt"
    "io/ioutil"
    "os"
    "path/filepath"
    "strings"
)

func main() {
    p := somePath()
    fmt.Println(p)

    sep := fmt.Sprintf("%c", filepath.Separator)
    p = strings.TrimSuffix(p, sep)

    fmt.Println(p)
}

func somePath() string {
    dir, err := ioutil.TempDir("", "")
    if err != nil {
        panic(err)
    }
    p := fmt.Sprintf("%s%c%s%c", dir, os.PathSeparator, "foobar", os.PathSeparator)
    return p
}

/tmp/065654753/foobar/
/tmp/065654753/foobar

---

fn main() {
    {
        let p = "/tmp/";

        let p = if ::std::path::is_separator(p.chars().last().unwrap()) {
            &p[0..p.len() - 1]
        } else {
            p
        };

        println!("{}", p);
    }
    
    {
        let p = "/tmp";

        let p = if ::std::path::is_separator(p.chars().last().unwrap()) {
            &p[0..p.len() - 1]
        } else {
            p
        };

        println!("{}", p);
    }
}

/tmp
/tmp

or

fn main() {
    {
        let mut p = "/tmp/";

        p = p.strip_suffix(std::path::is_separator).unwrap_or(p);

        println!("{}", p);
    }
    
    {
        let mut p = "/tmp";

        p = p.strip_suffix(std::path::is_separator).unwrap_or(p);

        println!("{}", p);
    }
}

/tmp
/tmp

152. <font color="0c0a3e">Turn a character into a string</font>

Create string s containing only the character c.

将字符转换成字符串

package main

import (
    "fmt"
    "os"
)

func main() {
    var c rune = os.PathSeparator
    fmt.Printf("%c \n", c)

    s := fmt.Sprintf("%c", c)
    fmt.Printf("%#v \n", s)
}

/ 
"/" 

---

fn main() {
    let c = 'a';
    
    let s = c.to_string();
    
    println!("{}", s);
}

a

153. <font color="0c0a3e">Concatenate string with integer</font>

Create string t as the concatenation of string s and integer i.

连接字符串和整数

package main

import (
    "fmt"
)

func main() {
    s := "Hello"
    i := 123

    t := fmt.Sprintf("%s%d", s, i)

    fmt.Println(t)
}

Hello123

---

fn main() {
    let s = "Foo";
    let i = 1;
    let t = format!("{}{}", s, i);
    
    println!("{}" , t);
}

Foo1

154. <font color="0c0a3e">Halfway between two hex color codes</font>

Find color c, the average between colors c1, c2.
c, c1, c2 are strings of hex color codes: 7 chars, beginning with a number sign # .
Assume linear computations, ignore gamma corrections.

求两个十六进制颜色代码的中间值

package main

import (
    "fmt"
    "strconv"
    "strings"
)

// For concision, halfway assume valid inputs.
// Caller must have explicitly checked that c1, c2 are well-formed color codes.
func halfway(c1, c2 string) string {
    r1, _ := strconv.ParseInt(c1[1:3], 16, 0)
    r2, _ := strconv.ParseInt(c2[1:3], 16, 0)
    r := (r1 + r2) / 2

    g1, _ := strconv.ParseInt(c1[3:5], 16, 0)
    g2, _ := strconv.ParseInt(c2[3:5], 16, 0)
    g := (g1 + g2) / 2

    b1, _ := strconv.ParseInt(c1[5:7], 16, 0)
    b2, _ := strconv.ParseInt(c2[5:7], 16, 0)
    b := (b1 + b2) / 2

    c := fmt.Sprintf("#%02X%02X%02X", r, g, b)
    return c
}

func main() {
    c1 := "#15293E"
    c2 := "#012549"

    if err := checkFormat(c1); err != nil {
        panic(fmt.Errorf("Wrong input %q: %v", c1, err))
    }
    if err := checkFormat(c2); err != nil {
        panic(fmt.Errorf("Wrong input %q: %v", c2, err))
    }

    c := halfway(c1, c2)
    fmt.Println("The average of", c1, "and", c2, "is", c)
}

func checkFormat(color string) error {
    if len(color) != 7 {
        return fmt.Errorf("Hex colors have exactly 7 chars")
    }
    if color[0] != '#' {
        return fmt.Errorf("Hex colors start with #")
    }
    isNotDigit := func(c rune) bool { return (c < '0' || c > '9') && (c < 'a' || c > 'f') }
    if strings.IndexFunc(strings.ToLower(color[1:]), isNotDigit) != -1 {
        return fmt.Errorf("Forbidden char")
    }
    return nil
}

The average of #15293E and #012549 is #0B2743

package main

import (
    "fmt"
    "strconv"
    "strings"
)

// For concision, halfway assume valid inputs.
// Caller must have explicitly checked that c1, c2 are well-formed color codes.
func halfway(c1, c2 string) string {
    var buf [7]byte
    buf[0] = '#'
    for i := 0; i < 3; i++ {
        sub1 := c1[1+2*i : 3+2*i]
        sub2 := c2[1+2*i : 3+2*i]
        v1, _ := strconv.ParseInt(sub1, 16, 0)
        v2, _ := strconv.ParseInt(sub2, 16, 0)
        v := (v1 + v2) / 2
        sub := fmt.Sprintf("%02X", v)
        copy(buf[1+2*i:3+2*i], sub)
    }
    c := string(buf[:])

    return c
}

func main() {
    c1 := "#15293E"
    c2 := "#012549"

    if err := checkFormat(c1); err != nil {
        panic(fmt.Errorf("Wrong input %q: %v", c1, err))
    }
    if err := checkFormat(c2); err != nil {
        panic(fmt.Errorf("Wrong input %q: %v", c2, err))
    }

    c := halfway(c1, c2)
    fmt.Println("The average of", c1, "and", c2, "is", c)
}

func checkFormat(color string) error {
    if len(color) != 7 {
        return fmt.Errorf("Hex colors have exactly 7 chars")
    }
    if color[0] != '#' {
        return fmt.Errorf("Hex colors start with #")
    }
    isNotDigit := func(c rune) bool { return (c < '0' || c > '9') && (c < 'a' || c > 'f') }
    if strings.IndexFunc(strings.ToLower(color[1:]), isNotDigit) != -1 {
        return fmt.Errorf("Forbidden char")
    }
    return nil
}

The average of #15293E and #012549 is #0B2743

---

use std::str::FromStr;
use std::fmt;

#[derive(Debug)]
struct Colour {
    r: u8,
    g: u8,
    b: u8
}

#[derive(Debug)]
enum ColourError {
    MissingHash,
    InvalidRed,
    InvalidGreen,
    InvalidBlue
}

impl fmt::Display for Colour {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "#{:02x}{:02x}{:02x}", self.r, self.g, self.b)
    }
}

impl FromStr for Colour {
    type Err = ColourError;
    
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if !s.starts_with('#') {
            Err(ColourError::MissingHash)
        } else {
            Ok(Colour {
                r: u8::from_str_radix(&s[1..3], 16).map_err(|_| ColourError::InvalidRed)?,
                g: u8::from_str_radix(&s[3..5], 16).map_err(|_| ColourError::InvalidGreen)?,
                b: u8::from_str_radix(&s[5..7], 16).map_err(|_| ColourError::InvalidBlue)?
            })
        }
    }
}

fn mid_colour(c1: &str, c2: &str) -> Result<String, ColourError> {
    let c1 = c1.parse::<Colour>()?;
    let c2 = c2.parse::<Colour>()?;
    let c = Colour {
        r: (((c1.r as u16) + (c2.r as u16))/2) as u8,
        g: (((c1.g as u16) + (c2.g as u16))/2) as u8,
        b: (((c1.b as u16) + (c2.b as u16))/2) as u8
    };
    Ok(format!("{}", c))
}

fn main() {
    println!("{}", mid_colour("#15293E", "#012549").unwrap())
}

#0b2743

155. <font color="0c0a3e">Delete file</font>

Delete from filesystem the file having path filepath.

删除文件

package main

import (
    "fmt"
    "io/ioutil"
    "os"
)

func main() {
    for _, filepath := range []string{
        "/tmp/foo.txt",
        "/tmp/bar.txt",
        "/tmp/foo.txt",
    } {
        err := os.Remove(filepath)
        if err == nil {
            fmt.Println("Removed", filepath)
        } else {
            fmt.Fprintln(os.Stderr, err)
        }
    }
}

func init() {
    err := ioutil.WriteFile("/tmp/foo.txt", []byte(`abc`), 0644)
    if err != nil {
        panic(err)
    }
}

Removed /tmp/foo.txt
remove /tmp/bar.txt: no such file or directory
remove /tmp/foo.txt: no such file or directory

---

use std::fs;

fn main() {
    let filepath = "/tmp/abc";

    println!("Creating {}", filepath);
    let _file = fs::File::create(filepath);

    let b = std::path::Path::new(filepath).exists();
    println!("{} exists: {}", filepath, b);

    println!("Deleting {}", filepath);
    let r = fs::remove_file(filepath);
    println!("{:?}", r);

    let b = std::path::Path::new(filepath).exists();
    println!("{} exists: {}", filepath, b);
}

Creating /tmp/abc
/tmp/abc exists: true
Deleting /tmp/abc
Ok(())
/tmp/abc exists: false

156. <font color="0c0a3e">Format integer with zero-padding</font>

Assign to string s the value of integer i in 3 decimal digits. Pad with zeros if i < 100. Keep all digits if i ≥ 1000.

用零填充格式化整数

package main

import (
    "fmt"
)

func main() {
    for _, i := range []int{
        0,
        8,
        64,
        256,
        2048,
    } {
        s := fmt.Sprintf("%03d", i)
        fmt.Println(s)
    }
}

000
008
064
256
2048

---

fn main() {
    let i = 1;
    let s = format!("{:03}", i);
    
    println!("{}", s);
    
    
    let i = 1000;
    let s = format!("{:03}", i);
    
    println!("{}", s);
}

001
1000

157. <font color="0c0a3e">Declare constant string</font>

Initialize a constant planet with string value "Earth".

声明常量字符串

package main

import (
    "fmt"
)

const planet = "Earth"

func main() {
    fmt.Println("We live on planet", planet)
}

We live on planet Earth

---

fn main() {
    const PLANET: &str = "Earth";
    
    println!("{}", PLANET);
}

Earth

158. <font color="0c0a3e">Random sublist</font>

Create a new list y from randomly picking exactly k elements from list x.

**It is assumed that x has at least k elements.
Each element must have same probability to be picked.
Each element from x must be picked at most once.
Explain if the original ordering is preserved or not.**

随机子列表

package main

import (
    "fmt"
    "math/rand"
)

func main() {
    type T string

    x := []T{"Alice", "Bob", "Carol", "Dan", "Eve", "Frank", "Grace", "Heidi"}
    k := 4

    y := make([]T, k)
    perm := rand.Perm(len(x))
    for i, v := range perm[:k] {
        y[i] = x[v]
    }

    fmt.Printf("%q", y)
}

["Frank" "Eve" "Carol" "Grace"]

---

use rand::prelude::*;
let mut rng = &mut rand::thread_rng();
let y = x.choose_multiple(&mut rng, k).cloned().collect::<Vec<_>>();

159. <font color="0c0a3e">Trie</font>

Define a Trie data structure, where entries have an associated value.
(Not all nodes are entries)

前缀树/字典树

package main

import (
    "fmt"
    "unicode/utf8"
)

type Trie struct {
    c        rune
    children map[rune]*Trie
    isLeaf   bool
    value    V
}

type V int

func main() {
    t := NewTrie(0)
    for s, v := range map[string]V{
        "to":  7,
        "tea": 3,
        "ted": 4,
        "ten": 12,
        "A":   15,
        "i":   11,
        "in":  5,
        "inn": 9,
    } {
        t.insert(s, v)
    }
    fmt.Println(t.startsWith("te", ""))
}

func NewTrie(c rune) *Trie {
    t := new(Trie)
    t.c = c
    t.children = map[rune]*Trie{}
    return t
}

func (t *Trie) insert(s string, value V) {
    if s == "" {
        t.isLeaf = true
        t.value = value
        return
    }
    c, tail := cut(s)
    child, exists := t.children[c]
    if !exists {
        child = NewTrie(c)
        t.children[c] = child
    }
    child.insert(tail, value)
}

func (t *Trie) startsWith(p string, accu string) []string {
    if t == nil {
        return nil
    }
    if p == "" {
        var result []string
        if t.isLeaf {
            result = append(result, accu)
        }
        for c, child := range t.children {
            rec := child.startsWith("", accu+string(c))
            result = append(result, rec...)
        }
        return result
    }
    c, tail := cut(p)
    return t.children[c].startsWith(tail, accu+string(c))
}

func cut(s string) (head rune, tail string) {
    r, size := utf8.DecodeRuneInString(s)
    return r, s[size:]
}

[ten tea ted]

---

struct Trie {
    val: String,
    nodes: Vec<Trie>
}

160. <font color="0c0a3e">Detect if 32-bit or 64-bit architecture</font>

Execute f32() if platform is 32-bit, or f64() if platform is 64-bit.
This can be either a compile-time condition (depending on target) or a runtime detection.

检测是32位还是64位架构

package main

import (
    "fmt"
    "strconv"
)

func main() {
    if strconv.IntSize == 32 {
        f32()
    }
    if strconv.IntSize == 64 {
        f64()
    }
}

func f32() {
    fmt.Println("I am 32-bit")
}

func f64() {
    fmt.Println("I am 64-bit")
}

I am 64-bit

---

fn main() {
    match std::mem::size_of::<&char>() {
        4 => f32(),
        8 => f64(),
        _ => {}
    }
}

fn f32() {
    println!("I am 32-bit");
}

fn f64() {
    println!("I am 64-bit");
}

I am 64-bit

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