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feat(interface): 添加Go语言接口教程和示例代码

添加了完整的Go语言接口教学内容，包括：

- README.md中详细介绍了Go语言接口的概念和特性
- 包含解耦、多态、扩展性等接口优势说明
- 提供面向接口编程的完整示例代码
- 展示了标准库中Reader、Writer等常用接口
- 实现了一个支持Reader和Writer接口的Buffer示例
- 在main.go中演示了接口的实际应用和类型断言用法
```
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day05/interface/README.md
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# Go语言接口 # Go语言接口
[课件](https://gitee.com/infraboard/go-course/blob/master/zh-cn/base/interface.md)
+ 解耦（Decoupling）：调用者不需要知道具体类型，只需要知道接口
+ 多态（Polymorphism）：不同类型可以有相同的接口，统一处理
+ 扩展性（Extensibility）：新增类型时，不需要修改已有代码
## 面向接口
```go
package main
import "fmt"
func main() {
//
dog := Dog{Name: "旺财"}
fmt.Println(dog.Speak())
//
cat := Cat{Name: "招财猫"}
fmt.Println(cat.Speak())
//
cow := Cow{Name: "小牛"}
fmt.Println(cow.Speak())
// 必须知道对象的对象, 才能调用, 面向具体类型来编写代码, 依赖具体类型, 耦合度高
// 没有一层统一抽象，上层业务逻辑，需要知道对象，才能调用，非常麻烦，高耦合
// speakers := []interface{}{dog, cat, cow}
// for _, speaker := range speakers {
// switch speaker.(type) {
// case Dog:
// fmt.Println(speaker.(Dog).Speak())
// case Cat:
// fmt.Println(speaker.(Cat).Speak())
// case Cow:
// fmt.Println(speaker.(Cow).Speak())
// }
// //...
// }
// 管理员，组织这些演技者，进行演讲
// interface 先制定规范， 底层系统按照规范进行实现，上层业务代码的编写将会是透明的，简单高效
// 这里的Speaker 和 Dog Cat Cow 都是type 他们是一种东西吗？
// speakers = []Dog{}{dog1,dog2, dog3}
// Speaker 是一种约束, 约束放入这个slice里面的对象，必须实现这个接口的所有方法
speakers := []Speaker{dog, cat, cow}
for _, speaker := range speakers {
fmt.Println(speaker.Speak())
}
// 只关注 方法(接口), 不关注 对象的编程的方式，就是面向接口
}
// 任何一个结构体 实现了这个接口的所有方法, 就实现了这个接口
// 接口是一层抽象, 只要实现了这个接口的所有方法, 就可以被当做这个接口来使用，屏蔽了底层系统
type Speaker interface {
Speak() string // 说话方法
GetName() string // 获取名字方法
}
// 2. 定义不同的类型
type Dog struct {
Name string
}
// 3. 实现接口方法
func (d Dog) Speak() string {
return "汪汪汪"
}
func (d Dog) GetName() string {
return d.Name
}
type Cat struct {
Name string
}
func (c Cat) Speak() string {
return "喵喵喵"
}
func (c Cat) GetName() string {
return c.Name
}
type Cow struct {
Name string
}
func (c Cow) Speak() string {
return "哞哞哞"
}
func (c Cow) GetName() string {
return c.Name
}
```
+ 解耦: 调用者不需要知道具体类型，只需要知道接口, fmt.Println(speaker.Speak())
+ 多态（Polymorphism）：不同类型可以有相同的接口，统一处理, []Speaker{dog, cat, cow}
+ 扩展性（Extensibility）：新增类型时，不需要修改已有代码
+ Go语言的接口实现是隐式的, 底层系统按照规范进行实现，上层业务代码的编写将会是透明的，简单高效
## 面向接口
```go
type Reader interface {
Read(p []byte) (n int, err error)
}
// Writer is the interface that wraps the basic Write method.
//
// Write writes len(p) bytes from p to the underlying data stream.
// It returns the number of bytes written from p (0 <= n <= len(p))
// and any error encountered that caused the write to stop early.
// Write must return a non-nil error if it returns n < len(p).
// Write must not modify the slice data, even temporarily.
//
// Implementations must not retain p.
type Writer interface {
Write(p []byte) (n int, err error)
}
// Closer is the interface that wraps the basic Close method.
//
// The behavior of Close after the first call is undefined.
// Specific implementations may document their own behavior.
type Closer interface {
Close() error
}
// Seeker is the interface that wraps the basic Seek method.
//
// Seek sets the offset for the next Read or Write to offset,
// interpreted according to whence:
// [SeekStart] means relative to the start of the file,
// [SeekCurrent] means relative to the current offset, and
// [SeekEnd] means relative to the end
// (for example, offset = -2 specifies the penultimate byte of the file).
// Seek returns the new offset relative to the start of the
// file or an error, if any.
//
// Seeking to an offset before the start of the file is an error.
// Seeking to any positive offset may be allowed, but if the new offset exceeds
// the size of the underlying object the behavior of subsequent I/O operations
// is implementation-dependent.
type Seeker interface {
Seek(offset int64, whence int) (int64, error)
}
// ReadWriter is the interface that groups the basic Read and Write methods.
type ReadWriter interface {
Reader
Writer
}
// ReadCloser is the interface that groups the basic Read and Close methods.
type ReadCloser interface {
Reader
Closer
}
// WriteCloser is the interface that groups the basic Write and Close methods.
type WriteCloser interface {
Writer
Closer
}
// ReadWriteCloser is the interface that groups the basic Read, Write and Close methods.
type ReadWriteCloser interface {
Reader
Writer
Closer
}
// ReadSeeker is the interface that groups the basic Read and Seek methods.
type ReadSeeker interface {
Reader
Seeker
}
// ReadSeekCloser is the interface that groups the basic Read, Seek and Close
// methods.
type ReadSeekCloser interface {
Reader
Seeker
Closer
}
// WriteSeeker is the interface that groups the basic Write and Seek methods.
type WriteSeeker interface {
Writer
Seeker
}
// ReadWriteSeeker is the interface that groups the basic Read, Write and Seek methods.
type ReadWriteSeeker interface {
Reader
Writer
Seeker
}
```
Io Reader和Writer接口
```go
// Reader is the interface that wraps the basic Read method.
//
// Read reads up to len(p) bytes into p. It returns the number of bytes
// read (0 <= n <= len(p)) and any error encountered. Even if Read
// returns n < len(p), it may use all of p as scratch space during the call.
// If some data is available but not len(p) bytes, Read conventionally
// returns what is available instead of waiting for more.
//
// When Read encounters an error or end-of-file condition after
// successfully reading n > 0 bytes, it returns the number of
// bytes read. It may return the (non-nil) error from the same call
// or return the error (and n == 0) from a subsequent call.
// An instance of this general case is that a Reader returning
// a non-zero number of bytes at the end of the input stream may
// return either err == EOF or err == nil. The next Read should
// return 0, EOF.
//
// Callers should always process the n > 0 bytes returned before
// considering the error err. Doing so correctly handles I/O errors
// that happen after reading some bytes and also both of the
// allowed EOF behaviors.
//
// If len(p) == 0, Read should always return n == 0. It may return a
// non-nil error if some error condition is known, such as EOF.
//
// Implementations of Read are discouraged from returning a
// zero byte count with a nil error, except when len(p) == 0.
// Callers should treat a return of 0 and nil as indicating that
// nothing happened; in particular it does not indicate EOF.
//
// Implementations must not retain p.
type Reader interface {
Read(p []byte) (n int, err error)
}
// Writer is the interface that wraps the basic Write method.
//
// Write writes len(p) bytes from p to the underlying data stream.
// It returns the number of bytes written from p (0 <= n <= len(p))
// and any error encountered that caused the write to stop early.
// Write must return a non-nil error if it returns n < len(p).
// Write must not modify the slice data, even temporarily.
//
// Implementations must not retain p.
type Writer interface {
Write(p []byte) (n int, err error)
}
```
如何实现一个buf
```go
func NewBuffer() *Buffer {
return &Buffer{
// 固定 1k 大小的缓冲区
buf: make([]byte, 1024),
dataLen: 0,
}
}
// 实现 Reader和 Writer方法
type Buffer struct {
buf []byte // 固定大小的缓冲区
dataLen int // 当前缓冲区中的数据量
}
func (b *Buffer) Read(p []byte) (n int, err error) {
if b.dataLen == 0 {
return 0, io.EOF
}
// 读取缓冲区中的数据
n = copy(p, b.buf[:b.dataLen])
fmt.Println("read: ", n)
// 移除已读数据（将未读数据前移）
copy(b.buf, b.buf[n:b.dataLen])
b.dataLen -= n
return n, nil
}
func (b *Buffer) Write(p []byte) (n int, err error) {
// 计算剩余空间
available := len(b.buf) - b.dataLen
if available == 0 {
// 缓冲区已满
return 0, io.ErrShortBuffer
}
// 只写入缓冲区能容纳的数据（固定大小，不扩展）
n = copy(b.buf[b.dataLen:], p)
b.dataLen += n
fmt.Printf("write: %d 字节, 缓冲区使用: %d/%d\n", n, b.dataLen, len(b.buf))
// 如果没能写入全部数据，返回 ErrShortBuffer
if n < len(p) {
return n, io.ErrShortBuffer
}
return n, nil
}
func (b *Buffer) String() string {
return string(b.buf[:b.dataLen])
}
// Reset 清空缓冲区
func (b *Buffer) Reset() {
b.dataLen = 0
}
```

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package main
import (
"fmt"
"io"
"os"
)
func main() {
//
dog := Dog{Name: "旺财"}
fmt.Println(dog.Speak())
//
cat := Cat{Name: "招财猫"}
fmt.Println(cat.Speak())
//
cow := Cow{Name: "小牛"}
fmt.Println(cow.Speak())
// 必须知道对象的对象, 才能调用, 面向具体类型来编写代码, 依赖具体类型, 耦合度高
// 没有一层统一抽象，上层业务逻辑，需要知道对象，才能调用，非常麻烦，高耦合
// speakers := []interface{}{dog, cat, cow}
// speakers := []any{dog, cat, cow}
// for _, speaker := range speakers {
// switch speaker.(type) {
// case Dog:
// fmt.Println(speaker.(Dog).Speak())
// case Cat:
// fmt.Println(speaker.(Cat).Speak())
// case Cow:
// fmt.Println(speaker.(Cow).Speak())
// case Person:
// fmt.Println(speaker.(Person).Speak())
// }
// //...
// }
person := Person{Name: "小明"}
// 管理员，组织这些演技者，进行演讲
// interface 先制定规范， 底层系统按照规范进行实现，上层业务代码的编写将会是透明的，简单高效
// 这里的Speaker 和 Dog Cat Cow 都是type 他们是一种东西吗？
// speakers = []Dog{}{dog1,dog2, dog3}
// Speaker 是一种约束, 约束放入这个slice里面的对象，必须实现这个接口的所有方法
speakers := []Speaker{dog, cat, cow, person}
for _, speaker := range speakers {
fmt.Println(speaker.Speak())
// 类型断言, 判断这个speaker是否是Dog类型, 如果是就调用Dog的GetName方法
// 断言成一个具体的类型来使用，一般不建议，因为这样就失去了接口的意义，接口的意义就是不关心具体类型，只关心方法
// if dog, ok := speaker.(Dog); ok {
// fmt.Println(dog.GetName())
// }
// 不安全方式（会panic）
// dog := a.(Dog) // 如果a不是Dog类型，会panic
// speaker.(Dog).GetName() // 只能调用接口的方法, 不能调用具体类型的方法
}
// 只关注 方法(接口), 不关注 对象的编程的方式，就是面向接口
// 1. 使用固定1k缓冲区循环读取文件并输出
buf := NewBuffer()
f, err := os.Open("main.go")
if err != nil {
panic(err)
}
defer f.Close()
// 循环读取：文件 -> 缓冲区 -> 标准输出
for {
// 清空缓冲区准备接收新数据
buf.Reset()
// 从文件读取最多1k数据到缓冲区
n, err := io.CopyN(buf, f, 1024)
if n > 0 {
// 将缓冲区的数据输出到标准输出
fmt.Printf("\n--- 读取了 %d 字节 ---\n", n)
io.Copy(os.Stdout, buf)
}
if err == io.EOF {
break
}
if err != nil {
panic(err)
}
}
}
// 任何一个结构体 实现了这个接口的所有方法, 就实现了这个接口
// 接口是一层抽象, 只要实现了这个接口的所有方法, 就可以被当做这个接口来使用，屏蔽了底层系统
type Speaker interface {
Speak() string // 说话方法
GetName() string // 获取名字方法
}
// 2. 定义不同的类型
type Dog struct {
Name string
}
// 3. 实现接口方法
func (d Dog) Speak() string {
return "汪汪汪"
}
func (d Dog) GetName() string {
return d.Name
}
type Cat struct {
Name string
}
func (c Cat) Speak() string {
return "喵喵喵"
}
func (c Cat) GetName() string {
return c.Name
}
type Cow struct {
Name string
}
func (c Cow) Speak() string {
return "哞哞哞"
}
func (c Cow) GetName() string {
return c.Name
}
// 标注自己实现了Speaker 不需要
type Person struct {
Name string
}
func (p Person) Speak() string {
return "hello"
}
func (p Person) GetName() string {
return p.Name
}
func NewBuffer() *Buffer {
return &Buffer{
// 固定 1k 大小的缓冲区
buf: make([]byte, 1024),
dataLen: 0,
}
}
// 实现 Reader和 Writer方法
type Buffer struct {
buf []byte // 固定大小的缓冲区
dataLen int // 当前缓冲区中的数据量
}
func (b *Buffer) Read(p []byte) (n int, err error) {
if b.dataLen == 0 {
return 0, io.EOF
}
// 读取缓冲区中的数据
n = copy(p, b.buf[:b.dataLen])
fmt.Println("read: ", n)
// 移除已读数据（将未读数据前移）
copy(b.buf, b.buf[n:b.dataLen])
b.dataLen -= n
return n, nil
}
func (b *Buffer) Write(p []byte) (n int, err error) {
// 计算剩余空间
available := len(b.buf) - b.dataLen
if available == 0 {
// 缓冲区已满
return 0, io.ErrShortBuffer
}
// 只写入缓冲区能容纳的数据（固定大小，不扩展）
n = copy(b.buf[b.dataLen:], p)
b.dataLen += n
fmt.Printf("write: %d 字节, 缓冲区使用: %d/%d\n", n, b.dataLen, len(b.buf))
// 如果没能写入全部数据，返回 ErrShortBuffer
if n < len(p) {
return n, io.ErrShortBuffer
}
return n, nil
}
func (b *Buffer) String() string {
return string(b.buf[:b.dataLen])
}
// Reset 清空缓冲区
func (b *Buffer) Reset() {
b.dataLen = 0
}
// end