Replies: 30 comments 48 replies
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select 定义A "select" statement chooses which of a set of possible send or receive operations will proceed. It looks similar to a "switch" statement but with the cases all referring to communication operations. 知识点
面向信仰编程
func main() {
ch := make(chan int)
go func() {
for range time.Tick(1 * time.Second) {
ch <- 0
}
}()
for {
select {
case <-ch:
println("case1")
case <-ch:
println("case2")
}
}
}for-select时break、continue、goto
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rangeMap 类型对于map类型遍历时，如果map没有初始化，只是map类型零值 package main
import (
"errors"
"fmt"
)
func main() {
fmt.Println("Hello, 世界")
succ, fail := t(false)
fmt.Println(succ, fail, succ == nil, fail == nil, len(succ), len(fail))
fmt.Printf("%p %p\n", succ, fail)
for k, v := range succ {
fmt.Println(k, v)
}
}
func t(ok bool) (succ map[string]int64, fail map[string]error) {
if ok {
succ["1"] = 1
fail["2"] = errors.New("2")
}
return
}
|
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for 循环A "for" statement specifies repeated execution of a block. There are three forms: The iteration may be controlled by a single condition, a "for" clause, or a "range" clause. For statements with single condition
For statements with for clause
分号分隔三段：
特殊用法
i := 0
for ; ; i++ {
fmt.Println(i)
if i > 10 {
break
}
}
for i := 0; ; i++ {
if i > 10 {
break
}
fmt.Println(i)
}
for i := 0; ; {
fmt.Println(i)
if i > 10 {
break
}
i++
}For statements with range clause
|
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Function函数A function type denotes the set of all functions with the same parameter and result types. The value of an uninitialized variable of function type is nil. |
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返回值不会进行初始化对于函数的命名返回值，go语言并不会初始化对于命名返回值变量，这里的变量将会是类型零值 例如对于map类型： package main
import (
"errors"
"fmt"
)
func main() {
fmt.Println("Hello, 世界")
succ, fail := t(false)
fmt.Println(succ, fail, succ == nil, fail == nil, len(succ), len(fail))
fmt.Printf("%p %p\n", succ, fail)
for k, v := range succ {
fmt.Println(k, v)
}
succ, fail = tt()
fmt.Println(succ, fail, succ == nil, fail == nil, len(succ), len(fail))
fmt.Printf("%p %p", succ, fail)
}
func t(ok bool) (succ map[string]int64, fail map[string]error) {
if ok {
succ["1"] = 1
fail["2"] = errors.New("2")
}
return
}
func tt() (map[string]int64, map[string]error) {
succ := make(map[string]int64)
fail := make(map[string]error)
return succ, fail
}结果： Hello, 世界
map[] map[] true true 0 0
0x0 0x0
map[] map[] false false 0 0
0xc00010c1e0 0xc00010c210 |
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类型零值为
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slice切片package main
import (
"fmt"
"sync"
cmap "github.com/orcaman/concurrent-map"
"github.com/panjf2000/ants/v2"
)
func main() {
pool, _ := ants.NewPool(500)
defer pool.Release()
fmt.Println("-", pool.Cap(), pool.Free(), pool.Running(), pool.Waiting())
fn := func(i int, succ, fail cmap.ConcurrentMap, wg *sync.WaitGroup) func() {
return func() {
defer wg.Done()
fmt.Println(i)
succ.Set(fmt.Sprintf("%d", i), i)
fail.Set(fmt.Sprintf("%d", i), i)
fmt.Println(&succ)
fmt.Printf("succ %p, fail %p", &succ, &fail)
fmt.Println("=", pool.Cap(), pool.Free(), pool.Running(), pool.Waiting())
}
}
succ := cmap.New()
fail := cmap.New()
fmt.Println(&succ)
fmt.Printf("succ %p %p, fail %p %p", succ, &succ, fail, &fail)
wg := sync.WaitGroup{}
for i, _ := range make([]int, 2000) {
wg.Add(1)
pool.Submit(fn(i, succ, fail, &wg))
}
wg.Wait()
fmt.Printf("succ %p, fail %p", &succ, &fail)
fmt.Println("*", pool.Cap(), pool.Free(), pool.Running(), pool.Waiting())
chk := map[int]struct{}{}
for i, _ := range make([]int, 2000) {
chk[i] = struct{}{}
}
fmt.Println(succ.Count())
for i, v := range succ.Items() {
fmt.Println(i, v)
}
fmt.Println("++++++++++")
fmt.Println(fail.Count())
for i, v := range fail.Items() {
fmt.Println(i, v)
}
} |
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new和make 定义
new 分配内存https://go.dev/ref/spec#Allocation make 创建slice、map和channel |
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iota常量iota 文档 https://go.dev/ref/spec#Iota
Go 为什么要设计 iota 常量？
iota 常用于以下的场景：
示例const (
c0 = iota // c0 == 0
c1 = iota // c1 == 1
c2 = iota // c2 == 2
)
const (
a = 1 << iota // a == 1 (iota == 0)
b = 1 << iota // b == 2 (iota == 1)
c = 3 // c == 3 (iota == 2, unused)
d = 1 << iota // d == 8 (iota == 3)
)
const (
u = iota * 42 // u == 0 (untyped integer constant)
v float64 = iota * 42 // v == 42.0 (float64 constant)
w = iota * 42 // w == 84 (untyped integer constant)
)
const x = iota // x == 0
const y = iota // y == 0
const (
bit0, mask0 = 1 << iota, 1<<iota - 1 // bit0 == 1, mask0 == 0 (iota == 0)
bit1, mask1 // bit1 == 2, mask1 == 1 (iota == 1)
_, _ // (iota == 2, unused)
bit3, mask3 // bit3 == 8, mask3 == 7 (iota == 3)
) |
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Go 语言 iota 的神奇力量iota 的应用场景
iota 的使用技巧和注意事项
|
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go get 问题fatal: Authentication failed for 'https://xxx.com/xx'
解决 git config --global --add url."[email protected]:".insteadOf "https://github.com/" |
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go高效编码工具转换和生成各种golang代码，提高编码效率 |
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Printlove |
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json2go |
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sql2gorm |
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yaml2go |
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contextPackage context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes. |
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Context源码，再度重相逢 |
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深度解密Go语言之context |
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官发博文：进一步阐明关于 context 的最佳实践 |
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走进Golang之Context的使用 |
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使用 Go 语言 context 包的取消功能 |
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Generics（泛型） Tutorial: Getting started with generics
|
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类型参数提案
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Go 1.18 泛型全面讲解：一篇讲清泛型的全部0. 泛型有着自己的适用场景
1. 一切从函数的形参和实参说起
2. Go泛型中新概念
3.1 其他的泛型类型所有类型定义都可使用类型形参，所以下面这种结构体以及接口的定义也可以使用类型形参： // 一个泛型类型的结构体。可用 int 或 sring 类型实例化
type MyStruct[T int | string] struct {
Name string
Data T
}
// 一个泛型接口(关于泛型接口在后半部分会详细讲解）
type IPrintData[T int | float32 | string] interface {
Print(data T)
}
// 一个泛型通道，可用类型实参 int 或 string 实例化
type MyChan[T int | string] chan T3.2 类型形参的互相套用
3.3 几种语法错误
3.4 特殊的泛型类型type Wow[T int | string] int
var a Wow[int] = 123 // 编译正确
var b Wow[string] = 123 // 编译正确
var c Wow[string] = "hello" // 编译错误，因为"hello"不能赋值给底层类型int
3.5 泛型类型的套娃泛型和普通的类型一样，可以互相嵌套定义出更加复杂的新类型 // 先定义个泛型类型 Slice[T]
type Slice[T int|string|float32|float64] []T
// ✗ 错误。泛型类型Slice[T]的类型约束中不包含uint, uint8
type UintSlice[T uint|uint8] Slice[T]
// ✓ 正确。基于泛型类型Slice[T]定义了新的泛型类型 FloatSlice[T] 。FloatSlice[T]只接受float32和float64两种类型
type FloatSlice[T float32|float64] Slice[T]
// ✓ 正确。基于泛型类型Slice[T]定义的新泛型类型 IntAndStringSlice[T]
type IntAndStringSlice[T int|string] Slice[T]
// ✓ 正确 基于IntAndStringSlice[T]套娃定义出的新泛型类型
type IntSlice[T int] IntAndStringSlice[T]
// 在map中套一个泛型类型Slice[T]
type WowMap[T int|string] map[string]Slice[T]
// 在map中套Slice[T]的另一种写法
type WowMap2[T Slice[int] | Slice[string]] map[string]T3.6 类型约束的两种选择type WowStruct[T int|string] struct {
Name string
Data []T
}
type WowStruct2[T []int|[]string] struct {
Name string
Data T
}3.7 匿名结构体不支持泛型// 下面的用法是错误的：
testCase := struct[T int|string] {
caseName string
got T
want T
}[int]{
caseName: "test OK",
got: 100,
want: 100,
}4. 泛型receiver
4.2 动态判断变量的类型
5. 泛型函数
5.1 匿名函数不支持泛型
5.2 既然支持泛型函数，那么泛型方法呢？
6. 变得复杂的接口通过 type Int interface {
int | int8 | int16 | int32 | int64
}
type Uint interface {
uint | uint8 | uint16 | uint32
}
type Float interface {
float32 | float64
}
type Slice[T Int | Uint | Float] []T // 使用 '|' 将多个接口类型组合6.1
|
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An Introduction To Generics |
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When To Use Generics |
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nilnil is a predeclared identifier representing the zero value for a pointer, channel, func, interface, map, or slice type. var nil Type // Type must be a pointer, channel, func, interface, map, or slice type
|
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Golang中的nil，没有人比我更懂nil！nil其实甚至不是golang的关键词，只是一个变量名 |
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nil 剖析1. 出镜率最高
2. 奇怪的案例在了解nil之前，我们继续遵循问题导向，先来看几个奇怪的或者说反直觉的案例
3. nil的剖析
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对于类型零值为nil的变量，使用前一定要特别注意有效，以防panic
|
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闭包
问题 1：如何实现闭包？ 闭包又是什么？你可以想象一下，在一个函数中存在对外来标识符的引用。所谓的外来标识符，既不代表当前函数的任何参数或结果，也不是函数内部声明的，它是直接从外边拿过来的。 还有个专门的术语称呼它，叫自由变量，可见它代表的肯定是个变量。实际上，如果它是个常量，那也就形成不了闭包了，因为常量是不可变的程序实体，而 闭包体现的却是由“不确定”变为“确定”的一个过程。 我们说的这个函数（以下简称闭包函数）就是因为引用了自由变量，而呈现出了一种“不确定”的状态，也叫“开放”状态。 也就是说，它的内部逻辑并不是完整的，有一部分逻辑需要这个自由变量参与完成，而后者到底代表了什么在闭包函数被定义的时候却是未知的。 即使对于像 Go 语言这种静态类型的编程语言而言，我们在定义闭包函数的时候最多也只能知道自由变量的类型。 在我们刚刚提到的genCalculator函数内部，实际上就实现了一个闭包，而genCalculator函数也是一个高阶函数。 func genCalculator(op operate) calculateFunc {
return func(x int, y int) (int, error) {
if op == nil {
return 0, errors.New("invalid operation")
}
return op(x, y), nil
}
}genCalculator函数只做了一件事，那就是定义一个匿名的、calculateFunc类型的函数并把它作为结果值返回。 |
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go module |
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Mapping versions to commitsmodule定义在仓库子目录时，module的版本标签名必须增加子目录前缀；参见 Mapping versions to commits
|
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Go Code Review Comments |
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sortPackage sort provides primitives for sorting slices and user-defined collections. |
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func SliceStable 和 func SliceIsSorted自定义比较器排序 定义使用一个用户提供的函数来对序列进行排序，函数类型为 func(i, j int) bool，其中参数 i, j 是序列中的索引 区别：
示例：family := []struct {
Name string
Age int
}{
{"Alice", 23},
{"David", 2},
{"Eve", 2},
{"Bob", 25},
}
// 用 age 排序，年龄相等的元素保持原始顺序
sort.SliceStable(family, func(i, j int) bool {
return family[i].Age < family[j].Age
})
fmt.Println(family) // [{David 2} {Eve 2} {Alice 23} {Bob 25}]
//下面实现排序order by age asc, name desc，如果 age 和 name 都相等则保持原始排序
sort.SliceStable(family, func(i, j int) bool {
if family[i].Age != family[j].Age {
return family[i].Age < family[j].Age
}
return strings.Compare(family[i].Name, family[j].Name) == 1
})
fmt.Println(family) // [{Eve 2} {David 2} {Alice 23} {Bob 25}] |
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func Sort 和 func Stable排序任意数据结构 定义任何实现 type Interface 接口的数据结构，都可以使用这两个方法进行排序 type Interface interface {
Len() int
Less(i, j int) bool // i, j 是元素的索引
Swap(i, j int)
}区别
示例type Person struct {
Name string
Age int
}
type customSort struct {
p []*Person
less func(x, y *Person) bool
}
func (x customSort) Len() int {len(x.p)}
func (x customSort) Less(i, j int) bool { return x.less(x.p[i], x.p[j]) }
func (x customSort) Swap(i, j int) { x.p[i], x.p[j] = x.p[j], x.p[i] }
func main() {
persons := []Person{
{"David", 2},
{"Alice", 23},
{"Eve", 2},
{"Bob", 25},
}
sort.Sort(customSort{persons, func(x, y *Person) bool {
if x.Age != y.Age {
return x.Age < y.Age
}
if x.Name != y.Name {
return x.Name > y.Name
}
return false
}})
} |
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reflect 反射reflect包实现了运行时反射，允许程序操作任意类型的对象。典型的用法就是接受一个 调用 关于go里面反射的介绍，参考“反射定律”：https://golang.org/doc/articles/laws_of_reflection.html |
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Go reflection 三定律与最佳实践 |
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emptyInterfaceemptyInterface is the header for an interface{} value. type emptyInterface struct {
typ *rtype
word unsafe.Pointer
} |
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nonEmptyInterfacenonEmptyInterface is the header for an interface value with methods. type nonEmptyInterface struct {
// see ../runtime/iface.go:/Itab
itab *struct {
ityp *rtype // static interface type
typ *rtype // dynamic concrete type
hash uint32 // copy of typ.hash
_ [4]byte
fun [100000]unsafe.Pointer // method table
}
word unsafe.Pointer
} |
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Go语言反射编程指南 |
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DeepEqual
|
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interface 接口 |
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Go Data Structures: Interfaces |
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深入研究 Go interface 底层实现 |
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接口方法的调用1. 前提说明
type Writer interface {
Write(p []byte) (n int, err error)
}
// Discard 实现了Writer接口方法，可以成功写入但不会做任何事
var Discard Writer = discard{}2. 调用方式
|
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unsafe |
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struct 结构体结构体是一组命名元素（称为字段）的序列，每个字段都有名称和类型。字段名可以显式指定(IdentifierList)或隐式指定(EmbeddedField)。在结构体中，非空字段名必须是唯一的。 |
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嵌套struct匿名字段
struct嵌套
|
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Go 空结构体：零内存的魔力1. 什么是空结构体
2. 空结构体的特点
3. 空结构体的使用场景
|
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Method 方法A method is a function with a receiver. A method declaration binds an identifier, the method name, to a method, and associates the method with the receiver's base type.
|
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方法接收者的值类型和指针类型
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Go 内存模型 |
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Go 垃圾回收 |
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Go GC：了解便利背后的开销 |
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channel 类型 |
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channel 的 15 条规则和底层实现 |
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defer 语句 |
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为什么 defer 的执行顺序和注册顺序不同？ |
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panic · recover |
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Go语言的跨协程异常处理
|
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Goroutine 与 panic、recover 的小问题 |
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Time 时间Package time provides functionality for measuring and displaying time. The calendrical calculations always assume a Gregorian calendar, with no leap seconds. |
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学会 Go 中的时间处理时区问题
时区转换需要获取同一个 time.Time 在不同时区下的结果，我们可以使用它的 In 方法
时间瞬间 time.Timetype Time struct {
wall uint64
ext int64
loc *Location
}
持续时间 time.Durationtime.Duration 用于表示两个时间瞬间 time.Time 之间所经过的时间。它通过 int64 表示纳秒计数，能表示的极限大约为 290 年 // A Duration represents the elapsed time between two instants
// as an int64 nanosecond count. The representation limits the
// largest representable duration to approximately 290 years.
type Duration int64
时间计算
格式化时间Go 使用固定的时间（Go 语言的诞生时间）作为布局模板
|
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Go语言时区加载函数 initLocal()func initLocal() {
// consult $TZ to find the time zone to use.
// no $TZ means use the system default /etc/localtime.
// $TZ="" means use UTC.
// $TZ="foo" or $TZ=":foo" if foo is an absolute path, then the file pointed
// by foo will be used to initialize timezone; otherwise, file
// /usr/share/zoneinfo/foo will be used.
tz, ok := syscall.Getenv("TZ")
switch {
case !ok:
z, err := loadLocation("localtime", []string{"/etc"})
if err == nil {
localLoc = *z
localLoc.name = "Local"
return
}
case tz != "":
if tz[0] == ':' {
tz = tz[1:]
}
if tz != "" && tz[0] == '/' {
if z, err := loadLocation(tz, []string{""}); err == nil {
localLoc = *z
if tz == "/etc/localtime" {
localLoc.name = "Local"
} else {
localLoc.name = tz
}
return
}
} else if tz != "" && tz != "UTC" {
if z, err := loadLocation(tz, platformZoneSources); err == nil {
localLoc = *z
return
}
}
}
// Fall back to UTC.
localLoc.name = "UTC"
}
|
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超好用的开源time库 |
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Organizing a Go module |
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Go项目目录该怎么组织？官方终于出指南了！
|
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golang-standards/project-layout |
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Declarations and scope 声明和作用域 |
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2.7. 作用域
|
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隐蔽的逻辑问题
|
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go
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