131. Successive conditions
Execute f1 if condition c1 is true, or else f2 if condition c2 is true, or else f3 if condition c3 is true. Don't evaluate a condition when a previous condition was true.
连续条件判等
package main import ( "fmt" "strings" ) func conditional(x string) { switch { case c1(x): f1() case c2(x): f2() case c3(x): f3() } } func main() { conditional("dog Snoopy") conditional("fruit Raspberry") } func f1() { fmt.Println("I'm a Human") } func f2() { fmt.Println("I'm a Dog") } func f3() { fmt.Println("I'm a Fruit") } var c1, c2, c3 = prefixCheck("human"), prefixCheck("dog"), prefixCheck("fruit") func prefixCheck(prefix string) func(string) bool { return func(x string) bool { return strings.HasPrefix(x, prefix) } }
I'm a Dog I'm a Fruit
if c1 { f1() } else if c2 { f2() } else if c3 { f3() }
or
match true { _ if c1 => f1(), _ if c2 => f2(), _ if c3 => f3(), _ => (), }
132. Measure duration of procedure execution
Run procedure f, and return the duration of the execution of f.
度量程序执行时间
package main import ( "fmt" "regexp" "strings" "time" ) func clock(f func()) time.Duration { t := time.Now() f() return time.Since(t) } func f() { re := regexp.MustCompilePOSIX("|A+{300}") re.FindAllString(strings.Repeat("A", 299), -1) } func main() { d := clock(f) // The result is always zero in the playground, which has a fixed clock! // Try it on your workstation instead. fmt.Println(d) }
use std::time::Instant; let start = Instant::now(); f(); let duration = start.elapsed();
133. Case-insensitive string contains
Set boolean ok to true if string word is contained in string s as a substring, even if the case doesn't match, or to false otherwise.
不区分大小写的字符串包含
package main import ( "fmt" "strings" ) // Package _strings has no case-insensitive version of _Contains, so // we have to make our own. func containsCaseInsensitive(s, word string) bool { lowerS, lowerWord := strings.ToLower(s), strings.ToLower(word) ok := strings.Contains(lowerS, lowerWord) return ok } func main() { s := "Let's dance the macarena" word := "Dance" ok := containsCaseInsensitive(s, word) fmt.Println(ok) word = "dance" ok = containsCaseInsensitive(s, word) fmt.Println(ok) word = "Duck" ok = containsCaseInsensitive(s, word) fmt.Println(ok) }
true true false
extern crate regex; use regex::Regex; fn main() { let s = "Let's dance the macarena"; { let word = "Dance"; let re = Regex::new(&format!("(?i){}", regex::escape(word))).unwrap(); let ok = re.is_match(&s); println!("{}", ok); } { let word = "dance"; let re = Regex::new(&format!("(?i){}", regex::escape(word))).unwrap(); let ok = re.is_match(&s); println!("{}", ok); } { let word = "Duck"; let re = Regex::new(&format!("(?i){}", regex::escape(word))).unwrap(); let ok = re.is_match(&s); println!("{}", ok); } }
true true false
or
use regex::RegexBuilder; fn main() { let s = "FooBar"; let word = "foo"; let re = RegexBuilder::new(®ex::escape(word)) .case_insensitive(true) .build() .unwrap(); let ok = re.is_match(s); println!("{:?}", ok); }
or
fn main() { let s = "Let's dance the macarena"; { let word = "Dance"; let ok = s.to_ascii_lowercase().contains(&word.to_ascii_lowercase()); println!("{}", ok); } { let word = "dance"; let ok = s.to_ascii_lowercase().contains(&word.to_ascii_lowercase()); println!("{}", ok); } { let word = "Duck"; let ok = s.to_ascii_lowercase().contains(&word.to_ascii_lowercase()); println!("{}", ok); } }
true true false
134. Create a new list
创建一个新list
package main import ( "fmt" ) func main() { var a, b, c T = "This", "is", "wonderful" items := []T{a, b, c} fmt.Println(items) } type T string
fn main() { let (a, b, c) = (11, 22, 33); let items = vec![a, b, c]; println!("{:?}", items); }
135. Remove item from list, by its value
Remove at most 1 item from list items, having value x. This will alter the original list or return a new list, depending on which is more idiomatic. If there are several occurrences of x in items, remove only one of them. If x is absent, keep items unchanged.
移除列表中的值
package main import ( "fmt" ) func main() { items := []string{"a", "b", "c", "d", "e", "f"} fmt.Println(items) x := "c" for i, y := range items { if y == x { items = append(items[:i], items[i+1:]...) break } } fmt.Println(items) }
[a b c d e f] [a b d e f]
or
for i, y := range items { if y == x { copy(items[i:], items[i+1:]) items[len(items)-1] = nil items = items[:len(items)-1] break } }
if let Some(i) = items.first(&x) { items.remove(i); }
136. Remove all occurrences of a value from a list
Remove all occurrences of value x from list items. This will alter the original list or return a new list, depending on which is more idiomatic.
从列表中删除所有出现的值
package main import ( "fmt" ) func main() { items := []T{"b", "a", "b", "a", "r"} fmt.Println(items) var x T = "b" items2 := make([]T, 0, len(items)) for _, v := range items { if v != x { items2 = append(items2, v) } } fmt.Println(items2) } type T string
[b a b a r] [a a r]
or
package main import ( "fmt" ) func main() { items := []T{"b", "a", "b", "a", "r"} fmt.Println(items) x := T("b") j := 0 for i, v := range items { if v != x { items[j] = items[i] j++ } } items = items[:j] fmt.Println(items) } type T string
[b a b a r] [a a r]
or
package main import ( "fmt" "runtime" ) func main() { var items []*image { red := newUniform(rgb{0xFF, 0, 0}) white := newUniform(rgb{0xFF, 0xFF, 0xFF}) items = []*image{red, white, red} // Like the flag of Austria fmt.Println("items =", items) x := red j := 0 for i, v := range items { if v != x { items[j] = items[i] j++ } } for k := j; k < len(items); k++ { items[k] = nil } items = items[:j] } // At this point, red can be garbage collected printAllocInfo() fmt.Println("items =", items) // Not the original flag anymore... fmt.Println("items undelying =", items[:3]) } type image [1024][1024]rgb type rgb [3]byte func newUniform(color rgb) *image { im := new(image) for x := range im { for y := range im[x] { im[x][y] = color } } return im } func printAllocInfo() { var stats runtime.MemStats runtime.GC() runtime.ReadMemStats(&stats) fmt.Println("Bytes allocated (total):", stats.TotalAlloc) fmt.Println("Bytes still allocated: ", stats.Alloc) }
items = [0xc000180000 0xc000480000 0xc000180000] Bytes allocated (total): 6416688 Bytes still allocated: 3259024 items = [0xc000480000] items undelying = [0xc000480000 <nil> <nil>]
fn main() { let x = 1; let mut items = vec![1, 2, 3, 1, 2, 3]; items = items.into_iter().filter(|&item| item != x).collect(); println!("{:?}", items); }
137. Check if string contains only digits
Set boolean b to true if string s contains only characters in range '0'..'9', false otherwise.
检查字符串是否只包含数字
package main import ( "fmt" ) func main() { for _, s := range []string{ "123", "", "abc123def", "abc", "123.456", "123 456", } { b := true for _, c := range s { if c < '0' || c > '9' { b = false break } } fmt.Println(s, "=>", b) } }
123 => true => true abc123def => false abc => false 123.456 => false 123 456 => false
or
package main import ( "fmt" "strings" ) func main() { for _, s := range []string{ "123", "", "abc123def", "abc", "123.456", "123 456", } { isNotDigit := func(c rune) bool { return c < '0' || c > '9' } b := strings.IndexFunc(s, isNotDigit) == -1 fmt.Println(s, "=>", b) } }
123 => true => true abc123def => false abc => false 123.456 => false 123 456 => false
fn main() { let s = "1023"; let chars_are_numeric: Vec<bool> = s.chars().map(|c|c.is_numeric()).collect(); let b = !chars_are_numeric.contains(&false); println!("{}", b); }
or
fn main() { let b = "0129".chars().all(char::is_numeric); println!("{}", b); }
138. Create temp file
Create a new temporary file on filesystem.
创建一个新的临时文件
package main import ( "io/ioutil" "log" "os" ) func main() { content := []byte("Big bag of misc data") log.Println("Opening new temp file") tmpfile, err := ioutil.TempFile("", "example") if err != nil { log.Fatal(err) } tmpfilename := tmpfile.Name() defer os.Remove(tmpfilename) // clean up log.Println("Opened new file", tmpfilename) log.Println("Writing [[", string(content), "]]") if _, err := tmpfile.Write(content); err != nil { log.Fatal(err) } if err := tmpfile.Close(); err != nil { log.Fatal(err) } log.Println("Closed", tmpfilename) log.Println("Opening", tmpfilename) buffer, err := ioutil.ReadFile(tmpfilename) if err != nil { log.Fatal(err) } log.Println("Read[[", string(buffer), "]]") }
2009/11/10 23:00:00 Opening new temp file 2009/11/10 23:00:00 Opened new file /tmp/example067319278 2009/11/10 23:00:00 Writing [[ Big bag of misc data ]] 2009/11/10 23:00:00 Closed /tmp/example067319278 2009/11/10 23:00:00 Opening /tmp/example067319278 2009/11/10 23:00:00 Read[[ Big bag of misc data ]]
use tempdir::TempDir; use std::fs::File; let temp_dir = TempDir::new("prefix")?; let temp_file = File::open(temp_dir.path().join("file_name"))?;
139. Create temp directory
Create a new temporary folder on filesystem, for writing.
创建一个临时目录
package main import ( "fmt" "io/ioutil" "log" "os" "path/filepath" ) func main() { content := []byte("temporary file's content") dir, err := ioutil.TempDir("", "") if err != nil { log.Fatal(err) } defer os.RemoveAll(dir) // clean up inspect(dir) tmpfn := filepath.Join(dir, "tmpfile") err = ioutil.WriteFile(tmpfn, content, 0666) if err != nil { log.Fatal(err) } inspect(dir) } func inspect(dirpath string) { files, err := ioutil.ReadDir(dirpath) if err != nil { log.Fatal(err) } fmt.Println(dirpath, "contains", len(files), "files") }
/tmp/067319278 contains 0 files /tmp/067319278 contains 1 files
extern crate tempdir; use tempdir::TempDir; let tmp = TempDir::new("prefix")?;
140. Delete map entry
从map中删除某个key
package main import ( "fmt" ) func main() { m := map[string]int{ "uno": 1, "dos": 2, "tres": 3, } delete(m, "dos") delete(m, "cinco") fmt.Println(m) }
fn main() { use std::collections::HashMap; let mut m = HashMap::new(); m.insert(5, "a"); m.insert(17, "b"); println!("{:?}", m); m.remove(&5); println!("{:?}", m); }
{17: "b", 5: "a"} {17: "b"}
