目录标题
- 一、Pointer
-
- [1. Declaring pointers](#1. Declaring pointers)
- [2. Zero value of a pointer](#2. Zero value of a pointer)
- [3. Creating pointers using the new function](#3. Creating pointers using the new function)
- [4. Dereferencing a pointer](#4. Dereferencing a pointer)
- [5. Passing pointer to a function](#5. Passing pointer to a function)
- [6. Returning pointer from a function](#6. Returning pointer from a function)
- [7. Do not pass a pointer to an array as an argument to a function. Use slice instead.](#7. Do not pass a pointer to an array as an argument to a function. Use slice instead.)
- [8. Go does not support pointer arithmetic](#8. Go does not support pointer arithmetic)
- 二、Structs
-
- [1. Creating named structs](#1. Creating named structs)
- [2. Creating anonymous structs](#2. Creating anonymous structs)
- [3. Accessing individual fields of a struct](#3. Accessing individual fields of a struct)
- [4. Zero value of a struct](#4. Zero value of a struct)
- [5. Pointers to a struct](#5. Pointers to a struct)
- [6. Anonymous fields](#6. Anonymous fields)
- [7. Nested structs](#7. Nested structs)
- [8. Promoted fields](#8. Promoted fields)
- [9. Structs Equality](#9. Structs Equality)
- 三、Methods
-
- [1. Sample Method](#1. Sample Method)
- [2. Pointer Receivers VS Value Receivers](#2. Pointer Receivers VS Value Receivers)
- [3. Methods of anonymous struct fields](#3. Methods of anonymous struct fields)
- [4. Value receivers in methods VS Value arguments in functions](#4. Value receivers in methods VS Value arguments in functions)
- [5. Pointer receivers in methods VS Pointer arguments in functions](#5. Pointer receivers in methods VS Pointer arguments in functions)
- [6. Methods with non-struct receivers](#6. Methods with non-struct receivers)
一、Pointer
1. Declaring pointers
go
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func main() {
b := 255
var a *int = &b
fmt.Printf("Type of is %T\n", a) // 获取值的类型
fmt.Println("address of b is ", a) // 内存地址
fmt.Println(b, *a) // 两种方法指向值
}
// Type of is *int
// address of b is 0xc0000180c8
// 255 255
2. Zero value of a pointer
go
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a := 25
var b *int
if b == nil {
fmt.Println("b is", b)
b = &a // 指向a的内存地址
fmt.Println("b after initialization is", b)
}
// b is <nil>
// b after initialization is 0xc0000180c8
3. Creating pointers using the new function
go
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size := new(int)
fmt.Printf("Size value is %d, type is %T, address is %v\n", *size, size, size)
*size = 85
fmt.Println("New size value is", *size)
// Size value is 0, type is *int, address is 0xc0000a6058
// New size value is 85
4. Dereferencing a pointer
go
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b := 255
a := &b
fmt.Println("address of b is", a)
fmt.Println("value of b is", *a)
*a++
fmt.Println("new values is", b)
//address of b is 0xc0000180c8
//value of b is 255
//new values is 256
5. Passing pointer to a function
go
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package main
import (
"fmt"
)
func change(val *int) {
*val = 55
}
func main() {
a := 58
fmt.Println("value of a before function call is",a)
b := &a
change(b)
fmt.Println("value of a after function call is", a)
}
// value of a before function call is 58
// value of a after function call is 55
6. Returning pointer from a function
go
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func helloWorld() *int {
i := 5
return &i
}
func main{
d := helloWorld()
fmt.Println("value of d", d)
}
// value of d 0xc0000180c8
7. Do not pass a pointer to an array as an argument to a function. Use slice instead.
go
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package main
import (
"fmt"
)
func modify(arr *[3]int) {
(*arr)[0] = 90
}
func main() {
a := [3]int{89, 90, 91}
modify(&a)
fmt.Println(a)
}
// slice func
func modifys(sls []int) {
sls[0] = 90
}
a := [3]int{89, 90, 91}
modifys(a[:])
fmt.Println(a)
8. Go does not support pointer arithmetic
go
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b := [...]int{109, 110, 111}
p := &b
p++ // invalid operation: p++ (non-numeric type *[3]int)
// Go不支持指针算术，而其他语言如C和c++中存在指针算术
二、Structs
1. Creating named structs
go
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package main
import (
"fmt"
)
type Employee struct {
firstName string
lastName string
age int
salary int
}
func main() {
//creating struct specifying field names
emp1 := Employee{
firstName: "Sam",
age: 25,
salary: 500,
lastName: "Anderson",
}
//creating struct without specifying field names
emp2 := Employee{"Thomas", "Paul", 29, 800}
fmt.Println("Employee 1", emp1)
fmt.Println("Employee 2", emp2)
}
2. Creating anonymous structs
go
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package main
import (
"fmt"
)
func main() {
emp3 := struct {
firstName string
lastName string
age int
salary int
}{
firstName: "Andreah",
lastName: "Nikola",
age: 31,
salary: 5000,
}
fmt.Println("Employee 3", emp3)
}
3. Accessing individual fields of a struct
go
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package main
import (
"fmt"
)
type Employee struct {
firstName string
lastName string
age int
salary int
}
func main() {
emp6 := Employee{
firstName: "Sam",
lastName: "Anderson",
age: 55,
salary: 6000,
}
fmt.Println("First Name:", emp6.firstName)
fmt.Println("Last Name:", emp6.lastName)
fmt.Println("Age:", emp6.age)
fmt.Printf("Salary: $%d\n", emp6.salary)
emp6.salary = 6500
fmt.Printf("New Salary: $%d", emp6.salary)
}
// First Name: Sam
// Last Name: Anderson
// Age: 55
// Salary: $6000
// New Salary: $6500
4. Zero value of a struct
go
复制代码
package main
import (
"fmt"
)
type Employee struct {
firstName string
lastName string
age int
salary int
}
func main() {
emp5 := Employee{
firstName: "John",
lastName: "Paul",
}
fmt.Println("First Name:", emp5.firstName)
fmt.Println("Last Name:", emp5.lastName)
fmt.Println("Age:", emp5.age)
fmt.Println("Salary:", emp5.salary)
}
// First Name: John
// Last Name: Paul
// Age: 0
// Salary: 0
5. Pointers to a struct
go
复制代码
package main
import (
"fmt"
)
type Employee struct {
firstName string
lastName string
age int
salary int
}
func main() {
emp8 := &Employee{
firstName: "Sam",
lastName: "Anderson",
age: 55,
salary: 6000,
}
fmt.Println("First Name:", (*emp8).firstName)
fmt.Println("Age:", (*emp8).age)
}
// First Name: Sam
// Age: 55
6. Anonymous fields
go
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package main
import (
"fmt"
)
type Person struct {
string
int
}
func main() {
p1 := Person{
string: "naveen",
int: 50,
}
fmt.Println(p1.string)
fmt.Println(p1.int)
}
7. Nested structs
go
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package main
import (
"fmt"
)
type Address struct {
city string
state string
}
type Person struct {
name string
age int
address Address
}
func main() {
p := Person{
name: "Naveen",
age: 50,
address: Address{
city: "Chicago",
state: "Illinois",
},
}
fmt.Println("Name:", p.name)
fmt.Println("Age:", p.age)
fmt.Println("City:", p.address.city)
fmt.Println("State:", p.address.state)
}
// Name: Naveen
// Age: 50
// City: Chicago
// State: Illinois
go
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package main
import (
"fmt"
)
type Address struct {
city string
state string
}
type Person struct {
name string
age int
Address
}
func main() {
p := Person{
name: "Naveen",
age: 50,
Address: Address{
city: "Chicago",
state: "Illinois",
},
}
fmt.Println("Name:", p.name)
fmt.Println("Age:", p.age)
fmt.Println("City:", p.city) //city is promoted field
fmt.Println("State:", p.state) //state is promoted field
}
// Name: Naveen
// Age: 50
// City: Chicago
// State: Illinois
9. Structs Equality
go
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package main
import (
"fmt"
)
type name struct {
firstName string
lastName string
}
func main() {
name1 := name{
firstName: "Steve",
lastName: "Jobs",
}
name2 := name{
firstName: "Steve",
lastName: "Jobs",
}
if name1 == name2 {
fmt.Println("name1 and name2 are equal")
} else {
fmt.Println("name1 and name2 are not equal")
}
name3 := name{
firstName: "Steve",
lastName: "Jobs",
}
name4 := name{
firstName: "Steve",
}
if name3 == name4 {
fmt.Println("name3 and name4 are equal")
} else {
fmt.Println("name3 and name4 are not equal")
}
}
// name1 and name2 are equal
// name3 and name4 are not equal
三、Methods
1. Sample Method
go
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package main
import (
"fmt"
)
type Employee struct {
name string
salary int
currency string
}
func (e Employee) displaySalary() {
fmt.Printf("Salary of %s is %s%d", e.name, e.currency, e.salary)
} // displaySalary() method has Employee as the receiver type
func main() {
emp1 := Employee{
name: "Like",
salary: 9999,
currency: "$",
}
emp1.displaySalary()
}
// Salary of Like is $9999
2. Pointer Receivers VS Value Receivers
go
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package main
import "fmt"
type Employees struct {
name string
age int
}
func (e Employees) changeName(newName string) { // 值接收器
e.name = newName
}
func (e *Employees) changeAge(newAge int) { // 指针接收器 必须添加*号否则修改不成功
e.age = newAge
}
func main() {
e := Employees{
name: "Like",
age: 21,
}
fmt.Printf("Employees name brfore change: %s", e.name)
e.changeName("XiaoXiao")
fmt.Printf("\nEmployees name after change: %s", e.name)
fmt.Printf("\nEmployees age brfore change: %d", e.age)
//e.changeAge(18)
(&e).changeAge(19) // &e使用指针的方法接收
fmt.Printf("\nEmployees age after change: %d", e.age)
}
// Employees name brfore change: Like
// Employees name after change: Like
// Employees age brfore change: 21
// Employees age after change: 19
3. Methods of anonymous struct fields
go
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type address struct {
city string
state string
}
func (a address) fullAddress() {
fmt.Printf("Full address: %s， %s", a.city, a.state)
}
type person struct {
firstName string
lastName string
address
}
func main() {
p := person{
firstName: "Li",
lastName: "ke",
address: address{
city: "Los Angeles",
state: "California",
},
}
p.fullAddress()
}
// Full address: Los Angeles， California
4. Value receivers in methods VS Value arguments in functions
go
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type rectangle struct {
length int
width int
}
func area(r rectangle) {
fmt.Printf("Area Function result: %d\n", (r.length * r.width))
}
func (r rectangle) area() {
fmt.Printf("Area Method result: %d\n", (r.length * r.width))
}
func main() {
r := rectangle{
length: 10,
width: 5,
}
area(r)
r.area()
p := &r
p.area()
}
// Area Function result: 50
// Area Method result: 50
// Area Method result: 50
5. Pointer receivers in methods VS Pointer arguments in functions
go
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type rectangle struct {
length int
width int
}
func perimeter(r *rectangle) {
fmt.Println("perimeter function output:", 2*(r.length+r.width))
}
func (r *rectangle) perimeter() {
fmt.Println("perimeter method output:", 2*(r.length+r.width))
}
func main() {
r := rectangle{
length: 10,
width: 5,
}
p := &r //pointer to r
perimeter(p)
p.perimeter()
r.perimeter() //calling pointer receiver with a value
}
// perimeter function output: 30
// perimeter method output: 30
// perimeter method output: 30
6. Methods with non-struct receivers
go
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type myInt int
func (a myInt) add(b myInt) myInt {
return a + b
}
func main() {
num1 := myInt(5)
num2 := myInt(10)
sum := num1.add(num2)
fmt.Println("Sum is", sum)
}
// Sum is 15