快速解析字符串到运行时提供的其他类型？

Question

我试图构建一个更快的版本Convert.ChangeType。该类型在运行时提供。该函数用于从文本文件解析字符串等

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，它仍然在剖析最慢的部分。这是一种提高速度的方法吗？

Answer 1

将字符串转换为另一种类型本身就很昂贵。但是，Convert.ChangeType正在进行虚拟接口调用以及可以避免的装箱/拆箱。

下面是它在幕后做：

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); 
    } 
    } 
} 

下面是它的使用类型数组：

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) 
};