Question

Is it possible to create a method that takes a boxed value type and returns whether that value type is equal to the default for that type?

So I want to create a method with the following signature:

bool IsDefault(object boxedValueType);

Note: the following code will not work as T gets set to type object so default(T) will always be null.

bool IsDefault<T>(T input)
{
    return Equals(input, default(T));
}

Answer 1

With reflection, but it’s a slow method

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("1 = " + IsDefault(1));
        Console.WriteLine("0 = " + IsDefault(default(int)));

        Console.WriteLine("1.0 = " + IsDefault(1.0));
        Console.WriteLine("0.0 = " + IsDefault(default(double)));

        Console.WriteLine("Today = " + IsDefault(DateTime.Today));
        Console.WriteLine("1.1.1 = " + IsDefault(default(DateTime)));

        //Console.WriteLine(IsDefault(""));
        //Console.WriteLine(IsDefault(default(string)));

        Console.ReadKey();
    }

    static bool IsDefault(object boxedValueType)
    {
        if (boxedValueType == null) throw new ArgumentNullException("boxedValueType");

        var t = boxedValueType.GetType();
        if (!t.IsValueType) throw new ArgumentOutOfRangeException("boxedValueType");

        object def = Activator.CreateInstance(t);
        return boxedValueType.Equals(def);
    }
}