快速解析字符串到運行時提供的其他類型？

Question

我試圖構建一個更快的版本Convert.ChangeType。該類型在運行時提供。該函數用於從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。這是一種提高速度的方法嗎？

Answer 1

將字符串轉換爲另一種類型本身就很昂貴。但是，Convert.ChangeType正在進行虛擬接口調用以及可以避免的裝箱/拆箱。

下面是它在幕後做：

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); 
    } 
    } 
} 

下面是它的使用類型數組：

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) 
};