go编码指南

type S struct {
  data string
}

func (s S) Read() string {
  return s.data
}

func (s *S) Write(str string) {
  s.data = str
}

sVals := map[int]S{1: {"A"}}

// You can only call Read using a value
sVals[1].Read()

// This will not compile:
//  sVals[0].Write("test")

sPtrs := map[int]*S{1: {"A"}}

// You can call both Read and Write using a pointer
sPtrs[1].Read()
sPtrs[1].Write("test")
Similarly, an interface can be satisfied by a pointer, even if the method has a value receiver.

type F interface {
  f()
}

type S1 struct{}

func (s S1) f() {}

type S2 struct{}

func (s *S2) f() {}

s1Val := S1{}
s1Ptr := &S1{}
s2Val := S2{}
s2Ptr := &S2{}

var i F
i = s1Val
i = s1Ptr
i = s2Ptr

// The following doesn't compile, since s2Val is a value, and there is no value receiver for f.
//   i = s2Val

type smap struct {
  sync.Mutex

  data map[string]string
}

func newSMap() *smap {
  return &smap{
    data: make(map[string]string),
  }
}

func (m *smap) Get(k string) string {
  m.Lock()
  defer m.Unlock()

  return m.data[k]
}

type SMap struct {
  mu sync.Mutex

  data map[string]string
}

func NewSMap() *SMap {
  return &SMap{
    data: make(map[string]string),
  }
}

func (m *SMap) Get(k string) string {
  m.mu.Lock()
  defer m.mu.Unlock()

  return m.data[k]
}

func (d *Driver) SetTrips(trips []Trip) {
  d.trips = trips
}

trips := ...
d1.SetTrips(trips)

// 修改 d1.trips?
trips[0] = ...

// SetTrips sets the driver's trips.
// Note that the slice is captured by reference, the
// caller should take care of prevening unwanted aliasing.
func (d *Driver) SetTrips(trips []Trip) { d.trips = trips }

// or:

func (d *Driver) SetTrips(trips []Trip) {
  d.trips = make([]Trip, len(trips))
  copy(d.trips, trips)
}

trips := ...
d1.SetTrips(trips)

// 这时候我们可以修改trips[0]而不会对d1.trips造成影响。
trips[0] = ...

type Stats struct {
  sync.Mutex

  counters map[string]int
}

// Snapshot returns the current stats.
func (s *Stats) Snapshot() map[string]int {
  s.Lock()
  defer s.Unlock()

  return s.counters
}

// snapshot is no longer protected by the lock!
snapshot := stats.Snapshot()

type Stats struct {
  sync.Mutex

  counters map[string]int
}

func (s *Stats) Snapshot() map[string]int {
  s.Lock()
  defer s.Unlock()

  result := make(map[string]int, len(s.counters))
  for k, v := range s.counters {
    result[k] = v
  }
  return result
}

// Snapshot is now a copy.
snapshot := stats.Snapshot()

p.Lock()
if p.count < 10 {
  p.Unlock()
  return p.count
}

p.count++
newCount := p.count
p.Unlock()

return newCount

// easy to miss unlocks due to multiple returns

p.Lock()
defer p.Unlock()

if p.count < 10 {
  return p.count
}

p.count++
return p.count

// more readable

// Ought to be enough for anybody!
c := make(chan int, 64)

// Size of one
c := make(chan int, 1) // or
// Unbuffered channel, size of zero
c := make(chan int)

type Operation int

const (
  Add Operation = iota
  Subtract
  Multiply
)

// Add=0, Subtract=1, Multiply=2

type Operation int

const (
  Add Operation = iota + 1
  Subtract
  Multiply
)

// Add=1, Subtract=2, Multiply=3

type LogOutput int

const (
  LogToStdout LogOutput = iota
  LogToFile
  LogToRemote
)

// LogToStdout=0, LogToFile=1, LogToRemote=2

// package foo

func Open() error {
  return errors.New("could not open")
}

// package bar

if err := foo.Open(); err != nil {
  if err.Error() == "could not open" {
    // handle
  } else {
    panic("unknown error")
  }
}

// package foo

var ErrCouldNotOpen = errors.New("could not open")

func Open() error {
  return ErrCouldNotOpen
}

// package bar

if err := foo.Open(); err != nil {
  if errors.Is(err, foo.ErrCouldNotOpen) {
    // handle
  } else {
    return errors.Wrap(err, "unknown error")
  }
}

func open(file string) error {
  return fmt.Errorf("file %q not found", file)
}

func use() error {
  if err := open(); err != nil {
    if strings.Contains(err.Error(), "not found") {
      // handle
    } else {
      panic("unknown error")
    }
  }
}

type errNotFound struct {
  file string
}

func (e errNotFound) Error() string {
  return fmt.Sprintf("file %q not found", e.file)
}

func open(file string) error {
  return errNotFound{file: file}
}

func use() error {
  if err := open(); err != nil {
    var nfErr errNotFound
    if errors.As(err, &nfErr); ok {
      // handle
    } else {
      return errors.Wrap(err, "opening file")
    }
  }
}

s, err := store.New()
if err != nil {
    return errors.Newf(
        "failed to create new store: %s", err)
}

s, err := store.New()
if err != nil {
    return errors.Wrap(
        "new store", err)
}

t := i.(string)

t, ok := i.(string)
if !ok {
  // handle the error gracefully
}

func foo(bar string) {
  if len(bar) == 0 {
    panic("bar must not be empty")
  }
  // ...
}

func main() {
  if len(os.Args) != 2 {
    fmt.Println("USAGE: foo <bar>")
    os.Exit(1)
  }
  foo(os.Args[1])
}

func foo(bar string) error {
  if len(bar) == 0
    return errors.New("bar must not be empty")
  }
  // ...
  return nil
}

func main() {
  if len(os.Args) != 2 {
    fmt.Println("USAGE: foo <bar>")
    os.Exit(1)
  }
  if err := foo(os.Args[1]); err != nil {
    panic(err)
  }
}

// func TestFoo(t *testing.T)

f, err := ioutil.TempFile("", "test")
if err != nil {
  panic("failed to set up test")
}

// func TestFoo(t *testing.T)

f, err := ioutil.TempFile("", "test")
if err != nil {
  t.Fatal("failed to set up test")
}

for i := 0; i < b.N; i++ {
  s := fmt.Sprint(rand.Int())
}

for i := 0; i < b.N; i++ {
  s := strconv.Itoa(rand.Int())
}

for i := 0; i < b.N; i++ {
  w.Write([]byte("Hello world"))
}

data := []byte("Hello world")
for i := 0; i < b.N; i++ {
  w.Write(data)
}

func (s *someType) myFunctionName(
arg1 somepackage.SomeArgType, arg2 int, arg3 somepackage.SomeOtherType,
) (somepackage.SomeReturnType, error) {
...
}

func (s *someType) myFunctionName(
   arg1 somepackage.SomeArgType,
   arg2 int,
   arg3 somepackage.SomeOtherType,
) (somepackage.SomeReturnType, error) {
...
}

func (s *someType) myFunctionName(
  arg1 somepackage.SomeArgType, arg2 somepackage.SomeOtherType,
) (
  somepackage.SomeReturnType,
  somepackage.SomeOtherType,
  error,
) {
...
}

import "a"
import "b"

import (
  "a"
  "b"
)

const a = 1
const b = 2

var a = 1
var b = 2

type Area float64
type Volume float64

const (
  a = 1
  b = 2
)

var (
  a = 1
  b = 2
)

type (
  Area float64
  Volume float64
)

type Operation int

const (
  Add Operation = iota + 1
  Subtract
  Multiply
  ENV_VAR = "MY_ENV"
)

type Operation int

const (
  Add Operation = iota + 1
  Subtract
  Multiply
)

const ENV_VAR = "MY_ENV"

func f() string {
  var red = color.New(0xff0000)
  var green = color.New(0x00ff00)
  var blue = color.New(0x0000ff)

  ...
}

func f() string {
  var (
    red   = color.New(0xff0000)
    green = color.New(0x00ff00)
    blue  = color.New(0x0000ff)
  )

  ...
}

import (
  "fmt"
  "os"
  "go.uber.org/atomic"
  "golang.org/x/sync/errgroup"
)

import (
  "fmt"
  "os"

  "go.uber.org/atomic"
  "golang.org/x/sync/errgroup"
)

import (
  "net/http"

  client "example.com/client-go"
  trace "example.com/trace/v2"
)

import (
  "fmt"
  "os"

  nettrace "golang.net/x/trace"
)

import (
  "fmt"
  "os"
  "runtime/trace"

  nettrace "golang.net/x/trace"
)

func (s *something) Cost() {
  return calcCost(s.weights)
}

type something struct{ ... }

func calcCost(n int[]) int {...}

func (s *something) Stop() {...}

func newSomething() *something {
    return &something{}
}

type something struct{ ... }

func newSomething() *something {
    return &something{}
}

func (s *something) Cost() {
  return calcCost(s.weights)
}

func (s *something) Stop() {...}

func calcCost(n int[]) int {...}

for _, v := range data {
  if v.F1 == 1 {
    v = process(v)
    if err := v.Call(); err == nil {
      v.Send()
    } else {
      return err
    }
  } else {
    log.Printf("Invalid v: %v", v)
  }
}

for _, v := range data {
  if v.F1 != 1 {
    log.Printf("Invalid v: %v", v)
    continue
  }

  v = process(v)
  if err := v.Call(); err != nil {
    return err
  }
  v.Send()
}

var a int
if b {
  a = 100
} else {
  a = 10
}

a := 10
if b {
  a = 100
}

var _s string = F()

func F() string { return "A" }

var _s = F()
// Since F already states that it returns a string, we don't need to specify
// the type again.

func F() string { return "A" }

type myError struct{}

func (myError) Error() string { return "error" }

func F() myError { return myError{} }

var _e error = F()
// F returns an object of type myError but we want error.

k := User{"John", "Doe", true}

k := User{
    FirstName: "John",
    LastName: "Doe",
    Admin: true,
}

tests := []struct{
}{
  op Operation
  want string
}{
  {Add, "add"},
  {Subtract, "subtract"},
}

var s = "foo"

s := "foo"

func f(list []int) {
  filtered := []int{}
  for _, v := range list {
    if v > 10 {
      filtered = append(filtered, v)
    }
  }
}

func f(list []int) {
  var filtered []int
  for _, v := range list {
    if v > 10 {
      filtered = append(filtered, v)
    }
  }
}

nums := []int{}
// or, nums := make([]int)

if add1 {
  nums = append(nums, 1)
}

if add2 {
  nums = append(nums, 2)
}

var nums []int

if add1 {
  nums = append(nums, 1)
}

if add2 {
  nums = append(nums, 2)
}

err := f.Close()
if err != nil {
 return err
}

if err := f.Close(); err != nil {
 return err
}

if f, err := os.Open("f"); err == nil {
  _, err = io.WriteString(f, "data")
  if err != nil {
    return err
  }
  return f.Close()
} else {
  return err
}

f, err := os.Open("f")
if err != nil {
   return err
}

if _, err := io.WriteString(f, "data"); err != nil {
  return err
}

return f.Close()

// func printInfo(name string, isLocal, done bool)

printInfo("foo", true, true)

// func printInfo(name string, isLocal, done bool)

printInfo("foo", true /* isLocal */, true /* done */)

type Region int

const (
  UnknownRegion Region = iota
  Local
)

type Status int

const (
  StatusReady = iota + 1
  StatusDone
  // Maybe we will have a StatusInProgress in the future.
)

func printInfo(name string, region Region, status Status)

func endTxn(commit bool){}
OK:     endTxn(false /* commit */)
NOT OK: endTxn(false /* !commit */)
NOT OK: endTxn(false /* abort */)
// If you want to add an explanation to an argument, a suggested style is to
// include both the param name and the explanation with a dash between them:
OK: endTxn(false /* commit - we abort as we concluded above that we can't commit */)

func doSomething(shouldDoX bool) {
  if shouldDoX {
    doX()
  } else {
    doY()
  }
}

type EndTxnAction bool

const (
Commit EndTxnAction = false
Abort = true
)

func endTxn(action EndTxnAction) {}
is better than:

func endTxn(commit bool) {}

wantError := "unknown name:\"test\""

wantError := `unknown error:"test"`

sval := T{Name: "foo"}

// inconsistent
sptr := new(T)
sptr.Name = "bar"

sval := T{Name: "foo"}

sptr := &T{Name: "bar"}

msg := "unexpected values %v, %v\n"
fmt.Printf(msg, 1, 2)

const msg = "unexpected values %v, %v\n"
fmt.Printf(msg, 1, 2)

go vet -printfuncs=wrapf,statusf

package datadriven

// RunTest invokes a data-driven test. The test cases are contained in a
// separate test file and are dynamically loaded, parsed, and executed by this
// testing framework. By convention, test files are typically located in a
// sub-directory called "testdata". Each test file has the following format:
//
//   <command>[,<command>...] [arg | arg=val | arg=(val1, val2, ...)]...
//   <input to the command>
//   ----
//   <expected results>
//
// The command input can contain blank lines. However, by default, the expected
// results cannot contain blank lines. This alternate syntax allows the use of
// blank lines:
//
//   <command>[,<command>...] [arg | arg=val | arg=(val1, val2, ...)]...
//   <input to the command>
//   ----
//   ----
//   <expected results>
//
//   <more expected results>
//   ----
//   ----
//
// To execute data-driven tests, pass the path of the test file as well as a
// function which can interpret and execute whatever commands are present in
// the test file. The framework invokes the function, passing it information
// about the test case in a TestData struct. The function then returns the
// actual results of the case, which this function compares with the expected
// results, and either succeeds or fails the test.
func RunTest(t *testing.T, path string, f func(d *TestData) string) 

// func TestSplitHostPort(t *testing.T)

host, port, err := net.SplitHostPort("192.0.2.0:8000")
require.NoError(t, err)
assert.Equal(t, "192.0.2.0", host)
assert.Equal(t, "8000", port)

host, port, err = net.SplitHostPort("192.0.2.0:http")
require.NoError(t, err)
assert.Equal(t, "192.0.2.0", host)
assert.Equal(t, "http", port)

host, port, err = net.SplitHostPort(":8000")
require.NoError(t, err)
assert.Equal(t, "", host)
assert.Equal(t, "8000", port)

host, port, err = net.SplitHostPort("1:8")
require.NoError(t, err)
assert.Equal(t, "1", host)
assert.Equal(t, "8", port)

// func TestSplitHostPort(t *testing.T)

tests := []struct{
  give     string
  wantHost string
  wantPort string
}{
  {
    give:     "192.0.2.0:8000",
    wantHost: "192.0.2.0",
    wantPort: "8000",
  },
  {
    give:     "192.0.2.0:http",
    wantHost: "192.0.2.0",
    wantPort: "http",
  },
  {
    give:     ":8000",
    wantHost: "",
    wantPort: "8000",
  },
  {
    give:     "1:8",
    wantHost: "1",
    wantPort: "8",
  },
}

for _, tt := range tests {
  t.Run(tt.give, func(t *testing.T) {
    host, port, err := net.SplitHostPort(tt.give)
    require.NoError(t, err)
    assert.Equal(t, tt.wantHost, host)
    assert.Equal(t, tt.wantPort, port)
  })
}

tests := []struct{
  give     string
  wantHost string
  wantPort string
}{
  // ...
}

for _, tt := range tests {
  // ...
}

// package db

func Connect(
  addr string,
  timeout time.Duration,
  caching bool,
) (*Connection, error) {
  // ...
}

// Timeout and caching must always be provided,
// even if the user wants to use the default.

db.Connect(addr, db.DefaultTimeout, db.DefaultCaching)
db.Connect(addr, newTimeout, db.DefaultCaching)
db.Connect(addr, db.DefaultTimeout, false /* caching */)
db.Connect(addr, newTimeout, false /* caching */)

type options struct {
  timeout time.Duration
  caching bool
}

// Option overrides behavior of Connect.
type Option interface {
  apply(*options)
}

type optionFunc func(*options)

func (f optionFunc) apply(o *options) {
  f(o)
}

func WithTimeout(t time.Duration) Option {
  return optionFunc(func(o *options) {
    o.timeout = t
  })
}

func WithCaching(cache bool) Option {
  return optionFunc(func(o *options) {
    o.caching = cache
  })
}

// Connect creates a connection.
func Connect(
  addr string,
  opts ...Option,
) (*Connection, error) {
  options := options{
    timeout: defaultTimeout,
    caching: defaultCaching,
  }

  for _, o := range opts {
    o.apply(&options)
  }

  // ...
}

// Options must be provided only if needed.

db.Connect(addr)
db.Connect(addr, db.WithTimeout(newTimeout))
db.Connect(addr, db.WithCaching(false))
db.Connect(
  addr,
  db.WithCaching(false),
  db.WithTimeout(newTimeout),
)