《go语言程序设计》学习（三）

一，单词替换

package main

import (
    "bufio"
    "fmt"
    "io"
    "io/ioutil"
    "log"
    "os"
    "path/filepath"
    "regexp"
    "strings"
)

var britishAmerican = "british-american.txt"

func init() {
    dir, _ := filepath.Split(os.Args[0])
    britishAmerican = filepath.Join(dir, britishAmerican)
    //fmt.Println("dir %s,file %s",dir,britishAmerican)
}

func main() {
    inFilename, outFilename, err := filenamesFromCommandLine()
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    inFile, outFile := os.Stdin, os.Stdout
    if inFilename != "" {
        if inFile, err = os.Open(inFilename); err != nil {
            log.Fatal(err)
        }
        defer inFile.Close()
    }
    if outFilename != "" {
        if outFile, err = os.Create(outFilename); err != nil {
            log.Fatal(err)
        }
        defer outFile.Close()
    }

    if err = americanise(inFile, outFile); err != nil {
        log.Fatal(err)
    }
}

func filenamesFromCommandLine() (inFilename, outFilename string, err error) {
    if len(os.Args) > 1 && (os.Args[1] == "-h" || os.Args[1] == "--help") {
        err = fmt.Errorf("usage :%s [<] infile.txt [>] outfile.txt",
            filepath.Base(os.Args[0]))
        return "", "", err
    }
    if len(os.Args) > 1 {
        inFilename = os.Args[1]
        if len(os.Args) > 2 {
            outFilename = os.Args[2]
        }
    }
    if inFilename != "" && inFilename == outFilename {
        log.Fatal("won't overwrite the infile")
    }
    return inFilename, outFilename, nil
}

func americanise(inFile io.Reader, outFile io.Writer) (err error) {
    reader := bufio.NewReader(inFile)
    writer := bufio.NewWriter(outFile)
    defer func() {
        if err == nil {
            err = writer.Flush()
        }
    }()

    var replacer func(string) string
    if replacer, err = makeReplacerFunction(britishAmerican); err != nil {
        return err
    }
    wordRx := regexp.MustCompile("[A-Za-z]+")
    eof := false
    for !eof {
        var line string
        line, err = reader.ReadString('
')
        if err == io.EOF {
            err = nil
            eof = true
        } else if err != nil {
            return err
        }
        line = wordRx.ReplaceAllStringFunc(line, replacer)
        if _, err = writer.WriteString(line); err != nil {

            return err
        }
    }
    return nil
}

func makeReplacerFunction(file string) (func(string) string, error) {
    rawBytes, err := ioutil.ReadFile(file)
    if err != nil {
        return nil, err
    }
    text := string(rawBytes)
    usForBritish := make(map[string]string)
    lines := strings.Split(text, "
")
    for _, line := range lines {
        fields := strings.Fields(line)
        if len(fields) == 2 {
            usForBritish[fields[0]] = fields[1]
        }
    }

    return func(word string) string {
        if usWord, found := usForBritish[word]; found {
            return usWord
        }
        return word
    }, nil
}

这次的格式终于没错

这个功能里面，我觉得有几个要点，一个是闭包，一个是正则的替换，还有个defer做后事～

简单理解一下闭包，在构造一个函数的时候，同时让这个函数自带了一些数据等其他内容，比如这里定义这个replacer函数的时候，首先定义replacer的私有数据map，然后返回了使用这个map的函数。这样在调用replacer的时候，就可以使用这个map点数据。（好像说的有点混乱。。）

正则和defer就没啥好说的了。。