Question

有没有办法简化这段代码？

fn parse(line: &str) -> Result<(usize, f64), String> {
    let mut it = line.split_whitespace();
    let n  = it.next().ok_or("Invalid line")?;
    let n = n.parse::<usize>().map_err(|e| e.to_string())?;
    let f = it.next().ok_or("Invalid line")?;
    let f = f.parse::<f64>().map_err(|e| e.to_string())?;
    Ok((n, f))
}

fn main() {       
    println!("Results: {:?}", parse("5 17.2").unwrap())
}

在实际代码中，我需要在线解析4个值，写.map_err(|e| e.to_string())

是很无聊的

据我了解，无法为std::convert::From / ParseIntError实施ParseFloatError - ＆gt; String，因为我的代码中没有定义任何类型，我是对的吗？

我看到了一种简化此代码的方法：

fn econv<E: ToString>(e: E) -> String {
    e.to_string()
}

并使用.map_err(econv)。还有其他选项可以简化我的代码吗？

Answer 1

嗯，一个不太可怕的选择就是创建一个抽象重复的函数：

use std::fmt::Display;
use std::iter::Iterator;
use std::str::FromStr;

fn parse_next<'a, Target, T>(it: &mut T) -> Result<Target, String>
    where
        T: Iterator<Item = &'a str>,
        Target: FromStr,
        <Target as FromStr>::Err: Display
{
    it.next().ok_or("Invalid line")?.parse::<Target>().map_err(|e| e.to_string())
}

fn parse(line: &str) -> Result<(usize, f64), String> {
    let mut it = line.split_whitespace();
    Ok((parse_next(&mut it)?, parse_next(&mut it)?))
}

fn main() {       
    println!("Results: {:?}", parse("5 17.2").unwrap())
}

Answer 2

我会介绍一种专用的错误类型。如果需要，我会在之后将错误转换为字符串：

import java.io.*;
import org.apache.poi.xwpf.usermodel.*;

import org.openxmlformats.schemas.wordprocessingml.x2006.main.CTP;
import org.openxmlformats.schemas.officeDocument.x2006.math.CTOMath;
import org.openxmlformats.schemas.officeDocument.x2006.math.CTOMathPara;

import org.w3c.dom.Node;

import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamSource;
import javax.xml.transform.stream.StreamResult;

import java.awt.Desktop;

import java.util.List;
import java.util.ArrayList;

/*
needs the full ooxml-schemas-1.3.jar as mentioned in https://poi.apache.org/faq.html#faq-N10025
*/

public class WordReadFormulas {

 static File stylesheet = new File("OMML2MML.XSL");
 static TransformerFactory tFactory = TransformerFactory.newInstance();
 static StreamSource stylesource = new StreamSource(stylesheet); 

 static String getMathML(CTOMath ctomath) throws Exception {
  Transformer transformer = tFactory.newTransformer(stylesource);

  Node node = ctomath.getDomNode();

  DOMSource source = new DOMSource(node);
  StringWriter stringwriter = new StringWriter();
  StreamResult result = new StreamResult(stringwriter);
  transformer.setOutputProperty("omit-xml-declaration", "yes");
  transformer.transform(source, result);

  String mathML = stringwriter.toString();
  stringwriter.close();

  //The native OMML2MML.XSL transforms OMML into MathML as XML having special name spaces.
  //We don't need this since we want using the MathML in HTML, not in XML.
  //So ideally we should changing the OMML2MML.XSL to not do so.
  //But to take this example as simple as possible, we are using replace to get rid of the XML specialities.
  mathML = mathML.replaceAll("xmlns:m=\"http://schemas.openxmlformats.org/officeDocument/2006/math\"", "");
  mathML = mathML.replaceAll("xmlns:mml", "xmlns");
  mathML = mathML.replaceAll("mml:", "");

  return mathML;
 }

 public static void main(String[] args) throws Exception {

  XWPFDocument document = new XWPFDocument(new FileInputStream("Formula.docx"));

  //storing the found MathML in a AllayList of strings
  List<String> mathMLList = new ArrayList<String>();

  //getting the formulas out of all body elements
  for (IBodyElement ibodyelement : document.getBodyElements()) {
   if (ibodyelement.getElementType().equals(BodyElementType.PARAGRAPH)) {
    XWPFParagraph paragraph = (XWPFParagraph)ibodyelement;
    for (CTOMath ctomath : paragraph.getCTP().getOMathList()) {
     mathMLList.add(getMathML(ctomath));
    }
    for (CTOMathPara ctomathpara : paragraph.getCTP().getOMathParaList()) {
     for (CTOMath ctomath : ctomathpara.getOMathList()) {
      mathMLList.add(getMathML(ctomath));
     }
    }
   } else if (ibodyelement.getElementType().equals(BodyElementType.TABLE)) {
    XWPFTable table = (XWPFTable)ibodyelement; 
    for (XWPFTableRow row : table.getRows()) {
     for (XWPFTableCell cell : row.getTableCells()) {
      for (XWPFParagraph paragraph : cell.getParagraphs()) {
       for (CTOMath ctomath : paragraph.getCTP().getOMathList()) {
        mathMLList.add(getMathML(ctomath));
       }
       for (CTOMathPara ctomathpara : paragraph.getCTP().getOMathParaList()) {
        for (CTOMath ctomath : ctomathpara.getOMathList()) {
         mathMLList.add(getMathML(ctomath));
        }
       }
      }
     }
    }
   }
  }

  document.close();

  //creating a sample HTML file 
  String encoding = "UTF-8";
  FileOutputStream fos = new FileOutputStream("result.html");
  OutputStreamWriter writer = new OutputStreamWriter(fos, encoding);
  writer.write("<!DOCTYPE html>\n");
  writer.write("<html lang=\"en\">");
  writer.write("<head>");
  writer.write("<meta charset=\"utf-8\"/>");

  //using MathJax for helping all browsers to interpret MathML
  writer.write("<script type=\"text/javascript\"");
  writer.write(" async src=\"https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=MML_CHTML\"");
  writer.write(">");
  writer.write("</script>");

  writer.write("</head>");
  writer.write("<body>");
  writer.write("<p>Following formulas was found in Word document: </p>");

  int i = 1;
  for (String mathML : mathMLList) {
   writer.write("<p>Formula" + i++ + ":</p>");
   writer.write(mathML);
   writer.write("<p/>");
  }

  writer.write("</body>");
  writer.write("</html>");
  writer.close();

  Desktop.getDesktop().browse(new File("result.html").toURI());

 }
}

如何在函数中多次简化将错误转换为字符串？

2 个答案: