quick overview

command line

Go is a tool for managing Go source code.

Usage:

    go <command> [arguments]

The commands are:

    bug         start a bug report
    build       compile packages and dependencies
    clean       remove object files and cached files
    doc         show documentation for package or symbol
    env         print Go environment information
    fix         update packages to use new APIs
    fmt         gofmt (reformat) package sources
    generate    generate Go files by processing source
    get         add dependencies to current module and install them
    install     compile and install packages and dependencies
    list        list packages or modules
    mod         module maintenance
    run         compile and run Go program
    test        test packages
    tool        run specified go tool
    version     print Go version
    vet         report likely mistakes in packages

Use "go help <command>" for more information about a command.

Additional help topics:

    buildconstraint build constraints
    buildmode       build modes
    c               calling between Go and C
    cache           build and test caching
    environment     environment variables
    filetype        file types
    go.mod          the go.mod file
    gopath          GOPATH environment variable
    gopath-get      legacy GOPATH go get
    goproxy         module proxy protocol
    importpath      import path syntax
    modules         modules, module versions, and more
    module-get      module-aware go get
    module-auth     module authentication using go.sum
    packages        package lists and patterns
    private         configuration for downloading non-public code
    testflag        testing flags
    testfunc        testing functions
    vcs             controlling version control with GOVCS

Use "go help <topic>" for more information about that topic.

比较常见的command line有:

go run [.]
go run [--race] [xxx.go]
go build [-o target] xxx.go
go mod init [module] #默认以当前文件名为module name
go mod tidy
go test
go get url
go doc
go fmt #我已经对它进行了优化，可以选择用 https://github.com/scott-x/myfmt

built-in types

• 布尔类型： bool
• 整型： int8，byte,int16,int,uint,uintptr等
• 浮点型: float32,float64
• 复数类型： complex64,complex128
• 字符串: string
• 字符类型:rune
• 错误类型: error

此外，golang也支持以下这些复合类型：

• 指针： pointer
• 数组： array
• 切片： slice
• 字典： map
• 通道： chan
• 结构体： struct
• 接口： interface

上面的数据类型可以归纳到下面这张图中:

zero value

int 0
uint 0
byte 0
float64 0
bool false
string "" (the empty string)
rune 0
struct nil

control flows

Conditionals:

if condition1 {
} else if condition2 {
} else {
}

switch i {
  case 0:
  case 1:
    fallthrough
  case 3:
    f()
  default:
    ...
}

loops:

//for loop
for i:=0; i<n; i++ {
  something
}
---
//for range 
for i,v := range array1 {
}
for key,value := range map1 { 
}

data structure

当用new去创建slice/array/map/instance的时候，它返回的是第一个元素的指针；当使用make的时候，它返回的是第一个元素

//const vs var
const a  = 1
var price, tax float64 
var x bool
var y,z int = 1,2
x,y,z := true, 123, "steve"
//array is a fixed number of continuous memory space
//slice is a resizable array
slice1 := []int{}
slice2 := append(slice1, 1) 
//make or new slice or array
slice1 := new([]int)
slice2 := make([]int, 10, 20)
slice3 := make([]int, 0)
slice4 := make([]int,10)
//map is key value pair
myMap :=make(map[string]string, 10). //define the length of the map
myMap :=make(map[string]string) //do not have to define the size
myMap["a"]="b" //assign value to its key
//notice that the element of the map could be a function, as follows
myFuncMap :=maps[string]func() int{
  "funcA": func() int{return 1},
}
//struct
type Person struct{
    Name string
    Age uint
    address Address
}

type Address struct {
  Province string
  City string
}

p1 :=new(Person)
p2 :=Person{}
p3 :=&Person{}

type A func(string) error
type B int

visiable & invisiable

首字母大写是可见的，反之不可见;

tips

同一包中: 属性、方法、结构体访问无限制, 可以直接拿来用; 不同包中： 首字母需大写, 其他包方可访问，尤其是结构体