Go语言旅行三 A Tour of Go

Basic types
基本类型

bool

string

int  int8  int16  int32  int64
uint uint8 uint16 uint32 uint64 uintptr

byte // alias for uint8

rune // alias for int32
     // represents a Unicode code point

float32 float64

complex64 complex128

package main

import (
	"math/cmplx"
	"fmt"
)

var (
	ToBe bool = false
	MaxInt uint64 = 1<<64 - 1
	z complex128 = cmplx.Sqrt(-5+12i)
)

func main() {
	const f = "%T(%v)\n"
	fmt.Printf(f, ToBe, ToBe)
	fmt.Printf(f, MaxInt, MaxInt)
	fmt.Printf(f, z, z)
}

输出：
bool(false)
uint64(18446744073709551615)
complex128((2+3i))

%T 是类型Type（%v）是值Value

Structs
结构体
A struct is a collection of fields.
结构体是很多字段的集合

package main

import "fmt"

type Vertex struct {
	X int
	Y int
}

func main() {
	fmt.Println(Vertex{1, 2})
}

输出：
{1 2}

Struct Fields
结构体字段
Struct fields are accessed using a dot.
结构体字段用点.访问

package main

import "fmt"

type Vertex struct {
	X int
	Y int
}

func main() {
	v := Vertex{1, 2}
	v.X = 4
	fmt.Println(v.X)
}

输出：
4

Pointers

Go has pointers, but no pointer arithmetic.
Go有指针，但是没有指针运算
Struct fields can be accessed through a struct pointer. The indirection through the pointer is transparent.
结构体字段能够通过结构体指针访问，很容易通过指针间接访问

package main

import "fmt"

type Vertex struct {
	X int
	Y int
}

func main() {
	p := Vertex{1, 2}
	q := &p
	q.X = 1e9
	fmt.Println(p)
}

输出：
{1000000000 2}

Struct Literals
结构体值
A struct literal denotes a newly allocated struct value by listing the values of its fields.
结构体值表示一个新分配结构体值通过列出它所有的字段值
You can list just a subset of fields by using the Name: syntax. (And the order of named fields is irrelevant.)
你也可以只通过名字语法勒出一部分字段值，顺序无所谓
The special prefix & constructs a pointer to a struct literal.
指定前缀&构造一个结构体字面值的指针

package main

import "fmt"

type Vertex struct {
	X, Y int
}

var (
	p = Vertex{1, 2}  // has type Vertex
	q = &Vertex{1, 2} // has type *Vertex
	r = Vertex{X: 1}  // Y:0 is implicit
	s = Vertex{}      // X:0 and Y:0
)

func main() {
	fmt.Println(p, q, r, s)
}

输出：
{1 2} &{1 2} {1 0} {0 0}

The new function
new函数
The expression new(T) allocates a zeroed T value and returns a pointer to it.
表达式 new（T）返回一个分配了0默认值的T类型的指针
var t *T = new(T)
or
t := new(T)

package main

import "fmt"

type Vertex struct {
	X, Y int
}

func main() {
	v := new(Vertex)
	fmt.Println(v)
	v.X, v.Y = 11, 9
	fmt.Println(v)
}

输出：
&{0 0}
&{11 9}

Maps

A map maps keys to values.
map匹配键和值
Maps must be created with make (not new) before use; the nil map is empty and cannot be assigned to.
Maps用之前必须用make创建，没有make的map是空的不能赋值

package main

import "fmt"

type Vertex struct {
	Lat, Long float64
}

var m map[string]Vertex

func main() {
	m = make(map[string]Vertex)
	m["Bell Labs"] = Vertex{
		40.68433, 74.39967,
	}
	fmt.Println(m["Bell Labs"])
}

输出：
{40.68433 74.39967}

Map literals are like struct literals, but the keys are required.
Map的字面值和结构体字面值一样，但是必须有键值

package main

import "fmt"

type Vertex struct {
	Lat, Long float64
}

var m = map[string]Vertex{
	"Bell Labs": Vertex{
		40.68433, -74.39967,
	},
	"Google": Vertex{
		37.42202, -122.08408,
	},
}

func main() {
	fmt.Println(m)
}

输出：
map[Google:{37.42202 -122.08408} Bell Labs:{40.68433 -74.39967}]

If the top-level type is just a type name, you can omit it from the elements of the literal.
如果顶级类型只是类型名的话，可以省略

package main

import "fmt"

type Vertex struct {
	Lat, Long float64
}

var m = map[string]Vertex{
	"Bell Labs": {40.68433, -74.39967},
	"Google":    {37.42202, -122.08408},
}

func main() {
	fmt.Println(m)
}

输出：
map[Google:{37.42202 -122.08408} Bell Labs:{40.68433 -74.39967}]

Mutating Maps
Maps变型

Insert or update an element in map m:
插入或修改map m的一个元素
m[key] = elem
Retrieve an element:
提取一个元素
elem = m[key]
Delete an element:
删除一个元素
delete(m, key)
Test that a key is present with a two-value assignment:
测试键里是否有值
elem, ok = m[key]
If key is in m, ok is true. If not, ok is false and elem is the zero value for the map's element type.
如果键有对应值，ok 是true，如果没有，ok是false，并且对应map's元素类型elem是0值
Similarly, when reading from a map if the key is not present the result is the zero value for the map's element type.
相似的是当从map取值的时候如果键值不存在，返回结果也是map's元素类型默认值

package main

import "fmt"

func main() {
	m := make(map[string]int)

	m["Answer"] = 42
	fmt.Println("The value:", m["Answer"])

	m["Answer"] = 48
	fmt.Println("The value:", m["Answer"])

	delete(m, "Answer")
	fmt.Println("The value:", m["Answer"])

	v, ok := m["Answer"]
	fmt.Println("The value:", v, "Present?", ok)
}

输出：
The value: 42
The value: 48
The value: 0
The value: 0 Present? false