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select {
case <-ch1:
  //...
case x:= <-ch2:
  //...
case ch3 <- y:
  //...
default:
  //...
}

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Example

• It needs to be in a file with a name like xxx_test.go
• The test function must start with the word Test
• The test function takes one argument only t *testing.T

package main

import "testing"

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// 更安全的随机
package main

import (
	"crypto/rand"
	// "encoding/base64"
	// "encoding/hex"
	"fmt"
)

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// 故意在接口中定义方法, 以防止其他类型无意中实现了该接口
type runtime.Error interface {
	error
    RuntimeError()
}

// or
type testing.TB interface {
	Error(args ...interface{})
	Errorf(format string, args ...interface{})

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func TrimSpace(s []byte) []byte {
  	b := s[:0] // 0 长度切片, len 虽然是0, 但是 cap 不为 0
	for _, x := range s {
		if X != ' ' {
			b = append(b, x)
		}
	}
	return b
}

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// 通过 sync/Once 实现单例
var (
	instance *singleton
	once 	 sync.Once
)

func Instance() *singleton {
	once.Do(func() {
		instance = &singleton{}
	})

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// [Sp|Fp|P]rintf 支持位置参数
package main

import "fmt"

func main() {
	fmt.Printf("%[3]v, %[2]v, %[1]v", 1, 2, 3) //3, 2, 1
}

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// 获取指定月份的天数
package main

import (
	"fmt"
	"time"
)

func days(year int, month time.Month) int {
	return time.Date(year, month+1, 0, 0, 0, 0, 0, time.UTC).Day()

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// 不通过反射, 通过类型断言判断一个类型是否含有某函数
package main

import (
	"fmt"
)

type A int
type B int

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// str[i] 取的是第 i 个 byte
package main

import (
	"fmt"
)

func main() {
	str1 := "abcdefg"
	str2 := "测试"