\d效率低于[0-9]

Question

今天我决定测试一下，结果我惊讶地发现（至少在C#正则表达式引擎中）\d似乎比其他两个没有太大区别的代码效率要低。下面是我测试输出的10000个由1000个随机字符组成的字符串，其中5077个实际包含一个数字：

Regex \d           took 00:00:00.2141226 result: 5077/10000
Regex [0-9]        took 00:00:00.1357972 result: 5077/10000  63.42 % of first
Regex [0123456789] took 00:00:00.1388997 result: 5077/10000  64.87 % of first

这对我来说是一个惊喜，有两个原因，如果有人能给我一些启示，我会很感兴趣：

1. 我本以为范围的实现会比集合的实现效率高得多。
2. 我不能理解为什么\d比[0-9]差。除了[0-9]的简写之外，\d还有其他内容吗？

下面是测试代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Text.RegularExpressions;

namespace SO_RegexPerformance
{
    class Program
    {
        static void Main(string[] args)
        {
            var rand = new Random(1234);
            var strings = new List<string>();
            //10K random strings
            for (var i = 0; i < 10000; i++)
            {
                //generate random string
                var sb = new StringBuilder();
                for (var c = 0; c < 1000; c++)
                {
                    //add a-z randomly
                    sb.Append((char)('a' + rand.Next(26)));
                }
                //in roughly 50% of them, put a digit
                if (rand.Next(2) == 0)
                {
                    //replace 1 char with a digit 0-9
                    sb[rand.Next(sb.Length)] = (char)('0' + rand.Next(10));
                }
                strings.Add(sb.ToString());
            }

            var baseTime = testPerfomance(strings, @"\d");
            Console.WriteLine();
            var testTime = testPerfomance(strings, "[0-9]");
            Console.WriteLine("  {0:P2} of first", testTime.TotalMilliseconds / baseTime.TotalMilliseconds);
            testTime = testPerfomance(strings, "[0123456789]");
            Console.WriteLine("  {0:P2} of first", testTime.TotalMilliseconds / baseTime.TotalMilliseconds);
        }

        private static TimeSpan testPerfomance(List<string> strings, string regex)
        {
            var sw = new Stopwatch();

            int successes = 0;

            var rex = new Regex(regex);

            sw.Start();
            foreach (var str in strings)
            {
                if (rex.Match(str).Success)
                {
                    successes++;
                }
            }
            sw.Stop();

            Console.Write("Regex {0,-12} took {1} result: {2}/{3}", regex, sw.Elapsed, successes, strings.Count);

            return sw.Elapsed;
        }
    }
}

Answer 1

\d检查所有Unicode数字，而[0-9]仅限于这10个字符。例如，波斯语数字是Unicode数字的一个例子，它与\d匹配，但不与[0-9]匹配。

您可以使用以下代码生成所有此类字符的列表：

var sb = new StringBuilder();
for(UInt16 i = 0; i < UInt16.MaxValue; i++)
{
    string str = Convert.ToChar(i).ToString();
    if (Regex.IsMatch(str, @"\d"))
        sb.Append(str);
}
Console.WriteLine(sb.ToString());

它生成：