Rust vs Go:常用语法对比(九)

题图来自 Golang vs Rust - The Race to Better and Ultimate Programming Language

161. <font color="0c0a3e">Multiply all the elements of a list</font>

Multiply all the elements of the list elements by a constant c

将list中的每个元素都乘以一个数

package main

import (
    "fmt"
)

func main() {
    const c = 5.5
    elements := []float64{2, 4, 9, 30}
    fmt.Println(elements)

    for i := range elements {
        elements[i] *= c
    }
    fmt.Println(elements)
}

[2 4 9 30]
[11 22 49.5 165]

---

fn main() {
    let elements: Vec<f32> = vec![2.0, 3.5, 4.0];
    let c = 2.0;

    let elements = elements.into_iter().map(|x| c * x).collect::<Vec<_>>();

    println!("{:?}", elements);
}

[4.0, 7.0, 8.0]

162. <font color="0c0a3e">Execute procedures depending on options</font>

execute bat if b is a program option and fox if f is a program option.

根据选项执行程序

package main

import (
    "flag"
    "fmt"
    "os"
)

func init() {
    // Just for testing in the Playground, let's simulate
    // the user called this program with command line
    // flags -f and -b
    os.Args = []string{"program", "-f", "-b"}
}

var b = flag.Bool("b", false, "Do bat")
var f = flag.Bool("f", false, "Do fox")

func main() {
    flag.Parse()
    if *b {
        bar()
    }
    if *f {
        fox()
    }
    fmt.Println("The end.")
}

func bar() {
    fmt.Println("BAR")
}

func fox() {
    fmt.Println("FOX")
}

BAR
FOX
The end.

---

if let Some(arg) = ::std::env::args().nth(1) {
    if &arg == "f" {
        fox();
    } else if &arg = "b" {
        bat();
    } else {
    eprintln!("invalid argument: {}", arg),
    }
} else {
    eprintln!("missing argument");
}

or

if let Some(arg) = ::std::env::args().nth(1) {
    match arg.as_str() {
        "f" => fox(),
        "b" => box(),
        _ => eprintln!("invalid argument: {}", arg),
    };
} else {
    eprintln!("missing argument");
}

163. <font color="0c0a3e">Print list elements by group of 2</font>

Print all the list elements, two by two, assuming list length is even.

两个一组打印数组元素

package main

import (
    "fmt"
)

func main() {
    list := []string{"a", "b", "c", "d", "e", "f"}

    for i := 0; i+1 < len(list); i += 2 {
        fmt.Println(list[i], list[i+1])
    }
}

a b
c d
e f

---

fn main() {
    let list = [1,2,3,4,5,6];
    for pair in list.chunks(2) {
        println!("({}, {})", pair[0], pair[1]);
    }
}

(1, 2)
(3, 4)
(5, 6)

164. <font color="0c0a3e">Open URL in default browser</font>

Open the URL s in the default browser.
Set boolean b to indicate whether the operation was successful.

在默认浏览器中打开链接

import "github.com/skratchdot/open-golang/open"
b := open.Start(s) == nil

or

func openbrowser(url string) {
    var err error

    switch runtime.GOOS {
    case "linux":
        err = exec.Command("xdg-open", url).Start()
    case "windows":
        err = exec.Command("rundll32", "url.dll,FileProtocolHandler", url).Start()
    case "darwin":
        err = exec.Command("open", url).Start()
    default:
        err = fmt.Errorf("unsupported platform")
    }
    if err != nil {
        log.Fatal(err)
    }

}

---

use webbrowser;
webbrowser::open(s).expect("failed to open URL");

165. <font color="0c0a3e">Last element of list</font>

Assign to variable x the last element of list items.

列表中的最后一个元素

package main

import (
    "fmt"
)

func main() {
    items := []string{ "what", "a", "mess" }
    
    x := items[len(items)-1]

    fmt.Println(x)
}

mess

---

fn main() {
    let items = vec![5, 6, 8, -20, 9, 42];
    let x = items[items.len()-1];
    println!("{:?}", x);
}

42

or

fn main() {
    let items = [5, 6, 8, -20, 9, 42];
    let x = items.last().unwrap();
    println!("{:?}", x);
}

42

166. <font color="0c0a3e">Concatenate two lists</font>

Create list ab containing all the elements of list a, followed by all elements of list b.

连接两个列表

package main

import (
    "fmt"
)

func main() {
    a := []string{"The ", "quick "}
    b := []string{"brown ", "fox "}

    ab := append(a, b...)

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

["The " "quick " "brown " "fox "]

or

package main

import (
    "fmt"
)

func main() {
    type T string

    a := []T{"The ", "quick "}
    b := []T{"brown ", "fox "}

    var ab []T
    ab = append(append(ab, a...), b...)

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

["The " "quick " "brown " "fox "]

or

package main

import (
    "fmt"
)

func main() {
    type T string

    a := []T{"The ", "quick "}
    b := []T{"brown ", "fox "}

    ab := make([]T, len(a)+len(b))
    copy(ab, a)
    copy(ab[len(a):], b)

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

["The " "quick " "brown " "fox "]

---

fn main() {
    let a = vec![1, 2];
    let b = vec![3, 4];
    let ab = [a, b].concat();
    println!("{:?}", ab);
}

[1, 2, 3, 4]

167. <font color="0c0a3e">Trim prefix</font>

Create string t consisting of string s with its prefix p removed (if s starts with p).

移除前缀

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "café-society"
    p := "café"

    t := strings.TrimPrefix(s, p)

    fmt.Println(t)
}

-society

---

fn main() {
    {
        let s = "pre_thing";
        let p = "pre_";
        let t = s.trim_start_matches(p);
        println!("{}", t);
    }
    {
        // Warning: trim_start_matches removes several leading occurrences of p, if present.
        let s = "pre_pre_thing";
        let p = "pre_";
        let t = s.trim_start_matches(p);
        println!("{}", t);
    }
}

thing
thing

or

fn main() {
    let s = "pre_pre_thing";
    let p = "pre_";

    let t = if s.starts_with(p) { &s[p.len()..] } else { s };
    println!("{}", t);
}

pre_thing

or

fn main() {
    {
        let s = "pre_thing";
        let p = "pre_";
        let t = s.strip_prefix(p).unwrap_or_else(|| s);
        println!("{}", t);
    }
    {
        // If prefix p is repeated in s, it is removed only once by strip_prefix
        let s = "pre_pre_thing";
        let p = "pre_";
        let t = s.strip_prefix(p).unwrap_or_else(|| s);
        println!("{}", t);
    }
}

thing
pre_thing

168. <font color="0c0a3e">Trim suffix</font>

Create string t consisting of string s with its suffix w removed (if s ends with w).

移除后缀

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "café-society"
    w := "society"

    t := strings.TrimSuffix(s, w)

    fmt.Println(t)
}

café-

---

fn main() {
    let s = "thing_suf";
    let w = "_suf";
    let t = s.trim_end_matches(w);
    println!("{}", t);

    let s = "thing";
    let w = "_suf";
    let t = s.trim_end_matches(w); // s does not end with w, it is left intact
    println!("{}", t);

    let s = "thing_suf_suf";
    let w = "_suf";
    let t = s.trim_end_matches(w); // removes several occurrences of w
    println!("{}", t);
}

thing
thing
thing

or

fn main() {
    let s = "thing_suf";
    let w = "_suf";
    let t = s.strip_suffix(w).unwrap_or(s);
    println!("{}", t);

    let s = "thing";
    let w = "_suf";
    let t = s.strip_suffix(w).unwrap_or(s); // s does not end with w, it is left intact
    println!("{}", t);

    let s = "thing_suf_suf";
    let w = "_suf";
    let t = s.strip_suffix(w).unwrap_or(s); // only 1 occurrence of w is removed
    println!("{}", t);
}

thing
thing
thing_suf

169. <font color="0c0a3e">String length</font>

Assign to integer n the number of characters of string s.

Make sure that multibyte characters are properly handled.
n can be different from the number of bytes of s.

字符串长度

package main

import "fmt"
import "unicode/utf8"

func main() {
    s := "Hello, 世界"
    n := utf8.RuneCountInString(s)

    fmt.Println(n)
}

9

---

fn main() {
    let s = "世界";

    let n = s.chars().count();

    println!("{} characters", n);
}

2 characters

170. <font color="0c0a3e">Get map size</font>

Set n to the number of elements stored in mymap.
This is not always equal to the map capacity.

获取map的大小

package main

import "fmt"

func main() {
    mymap := map[string]int{"a": 1, "b": 2, "c": 3}
    n := len(mymap)
    fmt.Println(n)
}

3

---

use std::collections::HashMap;

fn main() {
    let mut mymap: HashMap<&str, i32> = [("one", 1), ("two", 2)].iter().cloned().collect();
    mymap.insert("three", 3);

    let n = mymap.len();

    println!("mymap has {:?} entries", n);
}

mymap has 3 entries

171. <font color="0c0a3e">Add an element at the end of a list</font>

Append element x to the list s.

在list尾部添加元素

package main

import "fmt"

func main() {
    s := []int{1, 1, 2, 3, 5, 8, 13}
    x := 21

    s = append(s, x)

    fmt.Println(s)
}

[1 1 2 3 5 8 13 21]

---

fn main() {
    let mut s = vec![1, 2, 3];
    let x = 99;

    s.push(x);

    println!("{:?}", s);
}

[1, 2, 3, 99]

172. <font color="0c0a3e">Insert entry in map</font>

Insert value v for key k in map m.

向map中写入元素

package main

import "fmt"

func main() {
    m := map[string]int{"one": 1, "two": 2}
    k := "three"
    v := 3

    m[k] = v

    fmt.Println(m)
}

map[one:1 three:3 two:2]

---

use std::collections::HashMap;

fn main() {
    let mut m: HashMap<&str, i32> = [("one", 1), ("two", 2)].iter().cloned().collect();

    let (k, v) = ("three", 3);

    m.insert(k, v);

    println!("{:?}", m);
}

{"three": 3, "one": 1, "two": 2}

173. <font color="0c0a3e">Format a number with grouped thousands</font>

Number will be formatted with a comma separator between every group of thousands.

按千位格式化数字

package main

import (
    "fmt"

    "golang.org/x/text/language"
    "golang.org/x/text/message"
)

// The Playground doesn't work with import of external packages.
// However, you may copy this source and test it on your workstation.

func main() {
    p := message.NewPrinter(language.English)
    s := p.Sprintf("%d\n", 1000)

    fmt.Println(s)
    // Output:
    // 1,000
}

1,000

or

package main

import (
    "fmt"
    "github.com/floscodes/golang-thousands"
    "strconv"
)

// The Playground takes more time when importing external packages.
// However, you may want to copy this source and test it on your workstation.

func main() {
    n := strconv.Itoa(23489)
    s := thousands.Separate(n, "en")

    fmt.Println(s)
    // Output:
    // 23,489
}

23,489

---

use separator::Separatable;
println!("{}", 1000.separated_string());

174. <font color="0c0a3e">Make HTTP POST request</font>

Make a HTTP request with method POST to URL u

发起http POST请求

package main

import (
    "fmt"
    "io"
    "io/ioutil"
    "net"
    "net/http"
)

func main() {
    contentType := "text/plain"
    var body io.Reader
    u := "http://" + localhost + "/hello"

    response, err := http.Post(u, contentType, body)
    check(err)
    buffer, err := ioutil.ReadAll(response.Body)
    check(err)
    fmt.Println("POST response:", response.StatusCode, string(buffer))

    response, err = http.Get(u)
    check(err)
    buffer, err = ioutil.ReadAll(response.Body)
    check(err)
    fmt.Println("GET  response:", response.StatusCode, string(buffer))
}

const localhost = "127.0.0.1:3000"

func init() {
    http.HandleFunc("/hello", myHandler)
    startServer()
}

func myHandler(w http.ResponseWriter, r *http.Request) {
    if r.Method != "POST" {
        w.WriteHeader(http.StatusBadRequest)
        fmt.Fprintf(w, "Refusing request verb %q", r.Method)
        return
    }
    fmt.Fprintf(w, "Hello POST :)")
}

func startServer() {
    listener, err := net.Listen("tcp", localhost)
    check(err)

    go http.Serve(listener, nil)
}

func check(err error) {
    if err != nil {
        panic(err)
    }
}

POST response: 200 Hello Alice (POST)
GET  response: 400 Refusing request verb "GET"

or

package main

import (
    "fmt"
    "io/ioutil"
    "net"
    "net/http"
    "net/url"
)

func main() {
    formValues := url.Values{
        "who": []string{"Alice"},
    }
    u := "http://" + localhost + "/hello"

    response, err := http.PostForm(u, formValues)
    check(err)
    buffer, err := ioutil.ReadAll(response.Body)
    check(err)
    fmt.Println("POST response:", response.StatusCode, string(buffer))

    response, err = http.Get(u)
    check(err)
    buffer, err = ioutil.ReadAll(response.Body)
    check(err)
    fmt.Println("GET  response:", response.StatusCode, string(buffer))
}

const localhost = "127.0.0.1:3000"

func init() {
    http.HandleFunc("/hello", myHandler)
    startServer()
}

func myHandler(w http.ResponseWriter, r *http.Request) {
    if r.Method != "POST" {
        w.WriteHeader(http.StatusBadRequest)
        fmt.Fprintf(w, "Refusing request verb %q", r.Method)
        return
    }
    fmt.Fprintf(w, "Hello %s (POST)", r.FormValue("who"))
}

func startServer() {
    listener, err := net.Listen("tcp", localhost)
    check(err)

    go http.Serve(listener, nil)
}

func check(err error) {
    if err != nil {
        panic(err)
    }
}

---

[dependencies]
error-chain = "0.12.4"
reqwest = { version = "0.11.2", features = ["blocking"] }

use error_chain::error_chain;
use std::io::Read;
let client = reqwest::blocking::Client::new();
let mut response = client.post(u).body("abc").send()?;

175. <font color="0c0a3e">Bytes to hex string</font>

From array a of n bytes, build the equivalent hex string s of 2n digits.
Each byte (256 possible values) is encoded as two hexadecimal characters (16 possible values per digit).

字节转十六进制字符串

package main

import (
    "encoding/hex"
    "fmt"
)

func main() {
    a := []byte("Hello")

    s := hex.EncodeToString(a)

    fmt.Println(s)
}

48656c6c6f

---

use core::fmt::Write;

fn main() -> core::fmt::Result {
    let a = vec![22, 4, 127, 193];
    let n = a.len();
    
    let mut s = String::with_capacity(2 * n);
    for byte in a {
        write!(s, "{:02X}", byte)?;
    }
    
    dbg!(s);
    Ok(())
}

[src/main.rs:12] s = "16047FC1"

176. <font color="0c0a3e">Hex string to byte array</font>

From hex string s of 2n digits, build the equivalent array a of n bytes.
Each pair of hexadecimal characters (16 possible values per digit) is decoded into one byte (256 possible values).

十六进制字符串转字节数组

package main

import (
    "encoding/hex"
    "fmt"
    "log"
)

func main() {
    s := "48656c6c6f"

    a, err := hex.DecodeString(s)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(a)
    fmt.Println(string(a))
}

[72 101 108 108 111]
Hello

---

use hex::FromHex
let a: Vec<u8> = Vec::from_hex(s).expect("Invalid Hex String");

178. <font color="0c0a3e">Check if point is inside rectangle</font>

Set boolean b to true if if the point with coordinates (x,y) is inside the rectangle with coordinates (x1,y1,x2,y2) , or to false otherwise.

Describe if the edges are considered to be inside the rectangle.

检查点是否在矩形内

package main

import (
    "fmt"
    "image"
)

func main() {
    x1, y1, x2, y2 := 1, 1, 50, 100
    r := image.Rect(x1, y1, x2, y2)

    x, y := 10, 10
    p := image.Pt(x, y)
    b := p.In(r)
    fmt.Println(b)

    x, y = 100, 100
    p = image.Pt(x, y)
    b = p.In(r)
    fmt.Println(b)
}

true
false

---

struct Rect {
    x1: i32,
    x2: i32,
    y1: i32,
    y2: i32,
}

impl Rect {
    fn contains(&self, x: i32, y: i32) -> bool {
        return self.x1 < x && x < self.x2 && self.y1 < y && y < self.y2;
    }
}

179. <font color="0c0a3e">Get center of a rectangle</font>

Return the center c of the rectangle with coördinates(x1,y1,x2,y2)

获取矩形的中心

import "image"
c := image.Pt((x1+x2)/2, (y1+y2)/2)

---

struct Rectangle {
    x1: f64,
    y1: f64,
    x2: f64,
    y2: f64,
}

impl Rectangle {
    pub fn center(&self) -> (f64, f64) {
        ((self.x1 + self.x2) / 2.0, (self.y1 + self.y2) / 2.0)
    }
}

fn main() {
    let r = Rectangle {
        x1: 5.,
        y1: 5.,
        x2: 10.,
        y2: 10.,
    };
    
    println!("{:?}", r.center());
}

(7.5, 7.5)

180. <font color="0c0a3e">List files in directory</font>

Create list x containing the contents of directory d.
x may contain files and subfolders.
No recursive subfolder listing.

列出目录中的文件

package main

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

func main() {
    d := "/"

    x, err := ioutil.ReadDir(d)
    if err != nil {
        log.Fatal(err)
    }

    for _, f := range x {
        fmt.Println(f.Name())
    }
}

.dockerenv
bin
dev
etc
home
lib
lib64
proc
root
sys
tmp
tmpfs
usr
var

---

use std::fs;

fn main() {
    let d = "/etc";

    let x = fs::read_dir(d).unwrap();

    for entry in x {
        let entry = entry.unwrap();
        println!("{:?}", entry.path());
    }
}

or

fn main() {
    let d = "/etc";

    let x = std::fs::read_dir(d)
        .unwrap()
        .collect::<Result<Vec<_>, _>>()
        .unwrap();

    for entry in x {
        println!("{:?}", entry.path());
    }
}

"/etc/issue.net"
"/etc/bindresvport.blacklist"
"/etc/rc1.d"
"/etc/hostname"
"/etc/xattr.conf"
"/etc/resolv.conf"
"/etc/pam.conf"
"/etc/mke2fs.conf"
"/etc/e2scrub.conf"
"/etc/update-motd.d"
"/etc/terminfo"
"/etc/alternatives"
"/etc/ld.so.cache"
"/etc/networks"
"/etc/profile"
"/etc/debconf.conf"
"/etc/security"
"/etc/.pwd.lock"
"/etc/gai.conf"
"/etc/dpkg"
"/etc/rc3.d"
"/etc/fstab"
"/etc/gshadow"
"/etc/sysctl.conf"
"/etc/rc2.d"
"/etc/selinux"
"/etc/ld.so.conf.d"
"/etc/os-release"
"/etc/libaudit.conf"
"/etc/login.defs"
"/etc/skel"
"/etc/shells"
"/etc/rc4.d"
"/etc/cron.d"
"/etc/default"
"/etc/lsb-release"
"/etc/apt"
"/etc/debian_version"
"/etc/machine-id"
"/etc/deluser.conf"
"/etc/group"
"/etc/legal"
"/etc/rc6.d"
"/etc/init.d"
"/etc/sysctl.d"
"/etc/pam.d"
"/etc/passwd"
"/etc/rc5.d"
"/etc/bash.bashrc"
"/etc/hosts"
"/etc/rc0.d"
"/etc/environment"
"/etc/cron.daily"
"/etc/shadow"
"/etc/ld.so.conf"
"/etc/subgid"
"/etc/opt"
"/etc/logrotate.d"
"/etc/subuid"
"/etc/profile.d"
"/etc/adduser.conf"
"/etc/issue"
"/etc/rmt"
"/etc/host.conf"
"/etc/rcS.d"
"/etc/nsswitch.conf"
"/etc/systemd"
"/etc/kernel"
"/etc/mtab"
"/etc/shadow-"
"/etc/passwd-"
"/etc/subuid-"
"/etc/gshadow-"
"/etc/subgid-"
"/etc/group-"
"/etc/ethertypes"
"/etc/logcheck"
"/etc/gss"
"/etc/bash_completion.d"
"/etc/X11"
"/etc/perl"
"/etc/ca-certificates"
"/etc/protocols"
"/etc/ca-certificates.conf"
"/etc/python2.7"
"/etc/localtime"
"/etc/xdg"
"/etc/timezone"
"/etc/mailcap.order"
"/etc/emacs"
"/etc/ssh"
"/etc/magic.mime"
"/etc/services"
"/etc/ssl"
"/etc/ldap"
"/etc/rpc"
"/etc/mime.types"
"/etc/magic"
"/etc/mailcap"
"/etc/inputrc"

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