c# - 将字符串快速解析为运行时提供的其他类型？

Question

我正在尝试构建一个更快的 Convert.ChangeType 版本。该类型在运行时提供。该函数用于解析来自文本文件等的字符串。

public static object ConvertTo(Type t, string s)
{
    if (string.IsNullOrWhiteSpace(s) || s == null || Convert.IsDBNull(s)) return null;
    if (t == typeof(string)) return s; 
    if (t == typeof(DateTime)) { .... /* parse and return it */ }
    if (t == typeof(int)) { return int.Parse(s); }
    ....
    return Convert.ChangeType(s, t, CultureInfo.InvariantCulture); // Slowest
}

但是，它仍然是分析中最慢的部分。是提高速度更快的方法吗？

Answer 1

将字符串转换为另一种类型本质上是昂贵的。但是，Convert.ChangeType 正在执行您可以避免的虚拟接口(interface)调用和装箱/拆箱。

这是它在幕后所做的事情:

public static object ChangeType(object value, Type conversionType, IFormatProvider provider)
{
  if (conversionType == (Type) null)
    throw new ArgumentNullException("conversionType");
  if (value == null)
  {
    if (conversionType.IsValueType)
      throw new InvalidCastException(Environment.GetResourceString("InvalidCast_CannotCastNullToValueType"));
    else
      return (object) null;
  }
  else
  {
    IConvertible convertible = value as IConvertible;
    if (convertible == null)
    {
      if (value.GetType() == conversionType)
        return value;
      else
        throw new InvalidCastException(Environment.GetResourceString("InvalidCast_IConvertible"));
    }
    else
    {
      RuntimeType runtimeType = conversionType as RuntimeType;
      if (runtimeType == Convert.ConvertTypes[3])
        return (object) (bool) (convertible.ToBoolean(provider) ? 1 : 0);
      if (runtimeType == Convert.ConvertTypes[4])
        return (object) convertible.ToChar(provider);
      if (runtimeType == Convert.ConvertTypes[5])
        return (object) convertible.ToSByte(provider);
      if (runtimeType == Convert.ConvertTypes[6])
        return (object) convertible.ToByte(provider);
      if (runtimeType == Convert.ConvertTypes[7])
        return (object) convertible.ToInt16(provider);
      if (runtimeType == Convert.ConvertTypes[8])
        return (object) convertible.ToUInt16(provider);
      if (runtimeType == Convert.ConvertTypes[9])
        return (object) convertible.ToInt32(provider);
      if (runtimeType == Convert.ConvertTypes[10])
        return (object) convertible.ToUInt32(provider);
      if (runtimeType == Convert.ConvertTypes[11])
        return (object) convertible.ToInt64(provider);
      if (runtimeType == Convert.ConvertTypes[12])
        return (object) convertible.ToUInt64(provider);
      if (runtimeType == Convert.ConvertTypes[13])
        return (object) convertible.ToSingle(provider);
      if (runtimeType == Convert.ConvertTypes[14])
        return (object) convertible.ToDouble(provider);
      if (runtimeType == Convert.ConvertTypes[15])
        return (object) convertible.ToDecimal(provider);
      if (runtimeType == Convert.ConvertTypes[16])
        return (object) convertible.ToDateTime(provider);
      if (runtimeType == Convert.ConvertTypes[18])
        return (object) convertible.ToString(provider);
      if (runtimeType == Convert.ConvertTypes[1])
        return value;
      else
        return convertible.ToType(conversionType, provider);
    }
  }
}

这是它使用的类型数组:

internal static readonly RuntimeType[] ConvertTypes = new RuntimeType[19]
{
  (RuntimeType) typeof (Empty),
  (RuntimeType) typeof (object),
  (RuntimeType) typeof (DBNull),
  (RuntimeType) typeof (bool),
  (RuntimeType) typeof (char),
  (RuntimeType) typeof (sbyte),
  (RuntimeType) typeof (byte),
  (RuntimeType) typeof (short),
  (RuntimeType) typeof (ushort),
  (RuntimeType) typeof (int),
  (RuntimeType) typeof (uint),
  (RuntimeType) typeof (long),
  (RuntimeType) typeof (ulong),
  (RuntimeType) typeof (float),
  (RuntimeType) typeof (double),
  (RuntimeType) typeof (Decimal),
  (RuntimeType) typeof (DateTime),
  (RuntimeType) typeof (object),
  (RuntimeType) typeof (string)
};