Why is there a Convert.ToInt32(DateTime) method when the operation is "not supported"? [closed]

Question

The Convert.ToInt32(DateTime) method is documented to always throw an InvalidCastException because "This conversion is not supported."

If its not supported, why does it even exist? Wouldn't it make more sense to just not have that function?

Answer 1

Looking at the Convert implementation you can see that it relies on the IConvertible interface being implemented by the types that are being converted. The IConvertible interface forces a type to implement all conversion methods, and it is intended to work as you've described:

If there is no meaningful conversion to a common language runtime type, then a particular interface method implementation throws InvalidCastException.

So the method in question exists in Convert class probably because all IConvertibles have to have this method:

public static int ToInt32(DateTime value)
{
    return ((IConvertible)value).ToInt32(null);
}

So, similar to what others have noted seems that it's a matter of consistency with IConvertible interface and completeness. The Convert's implementation might even be generated, as it only relies on IConvertible.