检测通用参数的MaxValue

Question

我想编写应该使用的泛型类byte和ushort类型.我应该为这门课使用什么约束？如何检测MaxValue此类内部的属性？

class MyClass<T>   // where T: ???
{
    void Foo()
    {
        int maxValue = T.MaxValue;    // how can I do this?
    }
}

如果类是使用意外类型创建的,它不包含MaxValue属性,我不在乎 - 例如,我可以在运行时抛出异常.

Answer 1

一种方法是利用新dynamic关键字:

void Main()
{
    Test(10);
    Test(10.234);
    Test((Byte)42);
    Test(true);
}

public void Test<T>(T value)
    where T : struct
{
    T maxValue = MaxValue((dynamic)value);
    maxValue.Dump();
}

public int MaxValue(int dummy)
{
    return int.MaxValue;
}

public double MaxValue(double dummy)
{
    return double.MaxValue;
}

public byte MaxValue(byte dummy)
{
    return byte.MaxValue;
}

public object MaxValue(object dummy)
{
    // This method will catch all types that has no specific method
    throw new NotSupportedException(dummy.GetType().Name);
}

或者,您可以使用反射来获取MaxValue字段:

void Main()
{
    Test(10);
    Test(10.234);
    Test((Byte)42);
    Test(true);
}

public void Test<T>(T value)
    where T : struct
{
    FieldInfo maxValueField = typeof(T).GetField("MaxValue", BindingFlags.Public
        | BindingFlags.Static);
    if (maxValueField == null)
        throw new NotSupportedException(typeof(T).Name);
    T maxValue = (T)maxValueField.GetValue(null);
    maxValue.Dump();
}

您可以通过LINQPad测试这两个程序.

Answer 2

尝试这样的事情

    public T GetMaxValue()
    {
        object maxValue = default(T);
        TypeCode typeCode = Type.GetTypeCode(typeof(T));
        switch (typeCode)
        {
            case TypeCode.Byte:
                maxValue = byte.MaxValue;
                break;
            case TypeCode.Char:
                maxValue = char.MaxValue;
                break;
            case TypeCode.DateTime:
                maxValue = DateTime.MaxValue;
                break;
            case TypeCode.Decimal:
                maxValue = decimal.MaxValue;
                break;
            case TypeCode.Double:
                maxValue = decimal.MaxValue;
                break;
            case TypeCode.Int16:
                maxValue = short.MaxValue;
                break;
            case TypeCode.Int32:
                maxValue = int.MaxValue;
                break;
            case TypeCode.Int64:
                maxValue = long.MaxValue;
                break;
            case TypeCode.SByte:
                maxValue = sbyte.MaxValue;
                break;
            case TypeCode.Single:
                maxValue = float.MaxValue;
                break;
            case TypeCode.UInt16:
                maxValue = ushort.MaxValue;
                break;
            case TypeCode.UInt32:
                maxValue = uint.MaxValue;
                break;
            case TypeCode.UInt64:
                maxValue = ulong.MaxValue;
                break;
            default:
                maxValue = default(T);//set default value
                break;
        }

        return (T)maxValue;                             
    }