缓冲区写入方法的较短版本（DRY）

Question

我有这个方法，我想知道是否有一种实用且干净的方法来缩短这段代码： 这个练习来自Dart Apprentice: Beyond the Basics 一本书。

void main() {
  final lyric = '[00:12.34]Row, row, row your boat';

  final openBracketIndex = lyric.indexOf('[');
  final colonIndex = lyric.indexOf(':');
  final dotIndex = lyric.indexOf('.');
  final endBracketIndex = lyric.indexOf(']');

  final buffer = StringBuffer();
  buffer.write('minutes: ');
  buffer.write(lyric.substring(openBracketIndex + 1, colonIndex));
  buffer.write('\n');

  buffer.write('seconds: ');
  buffer.write(lyric.substring(colonIndex + 1, dotIndex));
  buffer.write('\n');

  buffer.write('hundredths: ');
  buffer.write(lyric.substring(dotIndex + 1, endBracketIndex));
  buffer.write('\n');

  buffer.write('lyrics: ');
  buffer.write(lyric.substring(endBracketIndex + 1));
  print(buffer);
}

输出为：

minutes: 00
seconds: 12
hundredths: 34
lyrics: Row, row, row your boat

Answer 1

您可以使用级联符号和

writeln

方法将代码缩短为：

void main() {
  final lyric = '[00:12.34]Row, row, row your boat';

  final openBracketIndex = lyric.indexOf('[');
  final colonIndex = lyric.indexOf(':');
  final dotIndex = lyric.indexOf('.');
  final endBracketIndex = lyric.indexOf(']');

  final buffer = StringBuffer()
    ..write('minutes: ')
    ..writeln(lyric.substring(openBracketIndex + 1, colonIndex))
    ..write('seconds: ')
    ..writeln(lyric.substring(colonIndex + 1, dotIndex))
    ..write('hundredths: ')
    ..writeln(lyric.substring(dotIndex + 1, endBracketIndex))
    ..write('lyrics: ')
    ..write(lyric.substring(endBracketIndex + 1));

  print(buffer);
}

如果我们允许我们在

StringBuilder

之外构建一些字符串，我们也可以进一步缩短它：

void main() {
  final lyric = '[00:12.34]Row, row, row your boat';

  final openBracketIndex = lyric.indexOf('[');
  final colonIndex = lyric.indexOf(':');
  final dotIndex = lyric.indexOf('.');
  final endBracketIndex = lyric.indexOf(']');

  final buffer = StringBuffer()
    ..writeln('minutes: ${lyric.substring(openBracketIndex + 1, colonIndex)}')
    ..writeln('seconds: ${lyric.substring(colonIndex + 1, dotIndex)}')
    ..writeln('hundredths: ${lyric.substring(dotIndex + 1, endBracketIndex)}')
    ..write('lyrics: ${lyric.substring(endBracketIndex + 1)}');

  print(buffer);
}

一个不太漂亮的解决方案是跳过

StringBuffer

，而是使用多行字符串作为模板：

void main() {
  final lyric = '[00:12.34]Row, row, row your boat';

  final openBracketIndex = lyric.indexOf('[');
  final colonIndex = lyric.indexOf(':');
  final dotIndex = lyric.indexOf('.');
  final endBracketIndex = lyric.indexOf(']');

  final string = '''
minutes: ${lyric.substring(openBracketIndex + 1, colonIndex)}
seconds: ${lyric.substring(colonIndex + 1, dotIndex)}
hundredths: ${lyric.substring(dotIndex + 1, endBracketIndex)}
lyrics: ${lyric.substring(endBracketIndex + 1)}
''';

  print(string);
}

Answer 2

虽然我通常不是第一个推荐正则表达式的人，但这看起来像是您应该使用正则表达式的一个杰出示例：解析已知的固定格式并提取部分。

并使用

writeln

添加换行符。

final lineRE = RegExp(r"^\[(\d+):(\d+)\.(\d+)\](.*)$");

void main() {
  final lyric = '[00:12.34]Row, row, row your boat';
  var parts = lineRE.firstMatch(lyric)!;
  return (StringBuffer()
    ..writeln('minutes: ${parts[1]}')
    ..writeln('seconds: ${parts[2]}')
    ..writeln('hundredths: ${parts[3]}')
    ..write('lyrics: ${parts[4]}')
  ).toString();
}

Answer 3

您可以使用级联符号来使用 StringBuffer 对象，以及 writeAll 语法：

void main() {
  final lyric = '[00:12.34]Row, row, row your boat';

  final openBracketIndex = lyric.indexOf('[');
  final colonIndex = lyric.indexOf(':');
  final dotIndex = lyric.indexOf('.');
  final endBracketIndex = lyric.indexOf(']');

  final buffer = StringBuffer()
    ..writeAll([
      'minutes: ',
      lyric.substring(openBracketIndex + 1, colonIndex),
      '\n',
      'seconds: ',
      lyric.substring(colonIndex + 1, dotIndex),
      '\n',
      'hundredths: ',
      lyric.substring(dotIndex + 1, endBracketIndex),
      '\n',
      'lyrics: ',
      lyric.substring(endBracketIndex + 1)]);
  
  print(buffer);
}