golang-101-hacks(24)——Decorate types to implement io.Reader interface

注：本文是对golang-101-hacks中文翻译

io包提供了一组便捷的读取函数和方法，但同时都需要参数满足io.Reader接口。请看下面的例子:

package main

import (
    "fmt"
    "io"
)

func main() {
    s := "Hello, world!"
    p := make([]byte, len(s))
    if _, err := io.ReadFull(s, p); err != nil {
        fmt.Println(err)
    } else {
        fmt.Printf("%s\n", p)
    }
} 

编译程序，会发生如下错误:
Compile above program and an error is generated:

read.go:11: cannot use s (type string) as type io.Reader in argument to io.ReadFull:
    string does not implement io.Reader (missing Read method)

io.ReadFull函数要求参数应该实现了' io.Reader '，但' string '类型没有Read()方法，所以需要对' s '变量做转换。将io.ReadFull(s, p)转换为io.ReadFull(strings.NewReader(s), p)：

package main

import (
    "fmt"
    "io"
    "strings"
)

func main() {
    s := "Hello, world!"
    p := make([]byte, len(s))
    if _, err := io.ReadFull(strings.NewReader(s), p); err != nil {
        fmt.Println(err)
    } else {
        fmt.Printf("%s\n", p)
    }
}

这次编译成功 运行结果如下

Hello, world!

strings.NewReader函数可以将字符串转换成strings.Reader

func (r *Reader) Read(b []byte) (n int, err error)  

Besides string, another common operation is to use bytes.NewReader to convert a byte slice into a bytes.Reader struct which satisfies io.Reader interface. Do some modifications on the above example:

 package main

import (
    "bytes"
    "fmt"
    "io"
    "strings"
)

func main() {
    s := "Hello, world!"
    p := make([]byte, len(s))
    if _, err := io.ReadFull(strings.NewReader(s), p); err != nil {
        fmt.Println(err)
    }

    r := bytes.NewReader(p)
    if b, err := r.ReadByte(); err != nil {
        fmt.Println(err)
    } else {
        fmt.Printf("%c\n", b)
    }
}

bytes.NewReader 将p切片转换为bytes.Reader结构。输出结果如下:

H