var q [3]int = [3]int{1, 2, 3}
var r [3]int = [3]int{1, 3}
fmt.Println(r[2])  // 0

q := [...]int{1, 2, 3}
fmt.Printf("%T\n", q)  // [3]int

q := [3]int{1,2,3}
q = [4]int{1,2,3,4}  // 编译错误

type Currency int

const (
    USD Currency = iota // 美元
    EUR                 // 欧元
    GBP                 // 英镑
    RMB                 // 人民币
)

symbol := [...]string{USD: "$", EUR: "€", GBP: "￡", RMB: "￥"}

fmt.Println(RMB, symbol[RMB]) // "3 ￥"

r := [...]int{99:-1}

a := [2]int{1, 2}
b := [...]int{1, 2}
c := [2]int{1, 3}
fmt.Println(a == b, a == c, b == c) // "true false false"
d := [3]int{1, 2}
fmt.Println(a == d) // compile error: cannot compare [2]int == [3]int

var a [3]int             // array of 3 integers
fmt.Println(a[0])        // print the first element
fmt.Println(a[len(a)-1]) // print the last element, a[2]

// Print the indices and elements.
for i, v := range a {
    fmt.Printf("%d %d\n", i, v)
}

// Print the elements only.
for _, v := range a {
    fmt.Printf("%d\n", v)
}

// reverse reverses a slice of ints in place.
func reverse(s []int) {
    for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
        s[i], s[j] = s[j], s[i]
    }
}

a := [...]int{0, 1, 2, 3, 4, 5}  // a 是数组, a[:] 是 slice
reverse(a[:])
fmt.Println(a) // "[5 4 3 2 1 0]"

func equal(x, y []string) bool {
    if len(x) != len(y) {
        return false
    }
    for i := range x {
        if x[i] != y[i] {
            return false
        }
    }
    return true
}

var runes []rune
for _, r := range "Hello, 世界" {
    runes = append(runes, r)
}
fmt.Printf("%q\n", runes) // "['H' 'e' 'l' 'l' 'o' ',' ' ' '世' '界']"

// Nonempty is an example of an in-place slice algorithm.
package main

import "fmt"

// nonempty returns a slice holding only the non-empty strings.
// The underlying array is modified during the call.
func nonempty(strings []string) []string {
    i := 0
    for _, s := range strings {
        if s != "" {
            strings[i] = s
            i++
        }
    }
    return strings[:i]
}

...

data := []string{"one", "", "three"}
fmt.Printf("%q\n", nonempty(data)) // `["one" "three"]`
fmt.Printf("%q\n", data)           // `["one" "three" "three"]`

ages := make(map[string]int)  // mapping from strings to ints

ages := map[string]int{
    "alice": 31,
    "charlie": 34,
}

ages := make(map[string]int)
ages["alice"] = 31
ages["charlie"] = 34

ages := map[string]int{}

var ages map[string]int
ages = make(map[string]int)

// 更新元素, 如果不存在该键, 则新增
ages["alice"] = 32

// 查询
fmt.Println(ages["alice"])  // "32"

// 删除元素
delete(ages, "alice")  // remove element ages["alice"]

age, ok := ages["bob"]
if !ok { /* "bob" is not a key in this map; age == 0. */ }

if age, ok := ages["bob"]; !ok { ... }

_ = &ages["bob"]  // compile error: cannot take address of map element

for name, age := range ages {
    fmt.Println("%s\t%d\n", name, age)
}

import "sort"

names := make([]string, 0, len(ages))
for name := range ages {
    names = append(names, name)
}
sort.Strings(names)
for _, name := range names {
    fmt.Printf("%s\t%d\n", name, ages[name])
}

var ages map[string]int
fmt.Println(ages == nil)    // "true"
fmt.Println(len(ages) == 0) // "true"
ages["carol"] = 21 // panic: assignment to entry in nil map

var ages map[string]int
ages = make(map[string]int)

// 或
ages := make(map[string]int)

func equal(x, y map[string]int) bool {
    if len(x) != len(y) {
        return false
    }
    for k, xv := range x {
        if yv, ok := y[k]; !ok || yv != xv {
            return false
        }
    }
    return true
}

var graph = make(map[string]map[string]bool)

func addEdge(from, to string) {
    edges := graph[from]
    if edges == nil {
        edges = make(map[string]bool)
        graph[from] = edges
    }
    edges[to] = true
}

func hasEdge(from, to string) bool {
    return graph[from][to]
}

type Employee struct {
    ID        int
    Name      string
    Address   string
    DoB       time.Time
    Position  string
    Salary    int
    ManagerID int
}

var dilbert Employee

dilbert.Salary -= 5000 // demoted, for writing too few lines of code

position := &dilbert.Position
*position = "Senior " + *position // promoted, for outsourcing to Elbonia

var employeeOfTheMonth *Employee = &dilbert
employeeOfTheMonth.Position += " (proactive team player)"

// 或者
(*employeeOfTheMonth).Position += " (proactive team player)"

type tree struct {
    value       int
    left, right *tree
}

// Sort sorts values in place.
func Sort(values []int) {
    var root *tree
    for _, v := range values {
        root = add(root, v)
    }
    appendValues(values[:0], root)
}

// appendValues appends the elements of t to values in order
// and returns the resulting slice.
func appendValues(values []int, t *tree) []int {
    if t != nil {
        values = appendValues(values, t.left)
        values = append(values, t.value)
        values = appendValues(values, t.right)
    }
    return values
}

func add(t *tree, value int) *tree {
    if t == nil {
        // Equivalent to return &tree{value: value}.
        t = new(tree)
        t.value = value
        return t
    }
    if value < t.value {
        t.left = add(t.left, value)
    } else {
        t.right = add(t.right, value)
    }
    return t
}

struct{}

func Scale(p Point, factor int) Point {
    return Point{p.X * factor, p.Y * factor}
}
fmt.Println(Scale(Point{1, 2}, 5)) // "{5 10}"

func Bonus(e *Employee, percent int) int {
    return e.Salary * percent / 100
}

type Point struct {
    X, Y int
}

type Circle struct {
    Center Point
    Radius int
}

type Wheel struct {
    Circle Circle
    Spokes int
}

var w Wheel
w.Circle.Center.X = 8
w.Circle.Center.Y = 8
w.Circle.Radius = 5
w.Spokes = 20

boolean         true
number          -273.15
string          "She said \"Hello, BF\""
array           ["gold", "silver", "bronze"]
object          {"year": 1980,
                 "event": "archery",
                 "medals": ["gold", "silver", "bronze"]}

type Movie struct {
    Title  string
    Year   int  `json:"released"`
    Color  bool `json:"color,omitempty"`
    Actors []string
}

var movies = []Movie{
    {Title: "Casablanca", Year: 1942, Color: false,
        Actors: []string{"Humphrey Bogart", "Ingrid Bergman"}},
    {Title: "Cool Hand Luke", Year: 1967, Color: true,
        Actors: []string{"Paul Newman"}},
    {Title: "Bullitt", Year: 1968, Color: true,
        Actors: []string{"Steve McQueen", "Jacqueline Bisset"}},
    // ...
}

data, err := json.Marshal(movies)
if err != nil {
    log.Fatalf("JSON marshaling failed: %s", err)
}
fmt.Printf("%s\n", data)

data, err := json.MarshalIndent(movies, "", "    ")
if err != nil {
    log.Fatalf("JSON marshaling failed: %s", err)
}
fmt.Printf("%s\n", data)

var titles []struct{ Title string }
if err := json.Unmarshal(data, &titles); err != nil {
    log.Fatalf("JSON unmarshaling failed: %s", err)
}
fmt.Println(titles) // "[{Casablanca} {Cool Hand Luke} {Bullitt}]"

// Package github provides a Go API for the GitHub issue tracker.
// See https://developer.github.com/v3/search/#search-issues.
package github

import "time"

const IssuesURL = "https://api.github.com/search/issues"

type IssuesSearchResult struct {
    TotalCount int `json:"total_count"`
    Items          []*Issue
}

type Issue struct {
    Number    int
    HTMLURL   string `json:"html_url"`
    Title     string
    State     string
    User      *User
    CreatedAt time.Time `json:"created_at"`
    Body      string    // in Markdown format
}

type User struct {
    Login   string
    HTMLURL string `json:"html_url"`
}

package github

import (
    "encoding/json"
    "fmt"
    "net/http"
    "net/url"
    "strings"
)

// SearchIssues queries the GitHub issue tracker.
func SearchIssues(terms []string) (*IssuesSearchResult, error) {
    q := url.QueryEscape(strings.Join(terms, " "))
    resp, err := http.Get(IssuesURL + "?q=" + q)
    if err != nil {
        return nil, err
    }

    // We must close resp.Body on all execution paths.
    // (Chapter 5 presents 'defer', which makes this simpler.)
    if resp.StatusCode != http.StatusOK {
        resp.Body.Close()
        return nil, fmt.Errorf("search query failed: %s", resp.Status)
    }

    var result IssuesSearchResult
    if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
        resp.Body.Close()
        return nil, err
    }
    resp.Body.Close()
    return &result, nil
}

// Issues prints a table of GitHub issues matching the search terms.
package main

import (
    "fmt"
    "log"
    "os"

    "gopl.io/ch4/github"
)

func main() {
    result, err := github.SearchIssues(os.Args[1:])
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("%d issues:\n", result.TotalCount)
    for _, item := range result.Items {
        fmt.Printf("#%-5d %9.9s %.55s\n",
            item.Number, item.User.Login, item.Title)
    }
}

const templ = `{{.TotalCount}} issues:
{{range .Items}}----------------------------------------
Number: {{.Number}}
User:   {{.User.Login}}
Title:  {{.Title | printf "%.64s"}}
Age:    {{.CreatedAt | daysAgo}} days
{{end}}`

func daysAgo(t time.Time) int {
    return int(time.Since(t).Hours() / 24)
}

report, err := template.New("report").
    Funcs(template.FuncMap{"daysAgo": daysAgo}).
    Parse(templ)
if err != nil {
    log.Fatal(err)
}

var report = template.Must(template.New("issuelist").
    Funcs(template.FuncMap{"daysAgo": daysAgo}).
    Parse(templ))

func main() {
    result, err := github.SearchIssues(os.Args[1:])
    if err != nil {
        log.Fatal(err)
    }
    if err := report.Execute(os.Stdout, result); err != nil {
        log.Fatal(err)
    }
}