C#: How can DateTime.Now be just an attribute?

Question

Hi

I'm trying to understand how the implementation of the Now attribute in DateTime works. My background is mainly Python and Haskell so I can't by my life understand how the Now attribute can "return" different values depending on when you use it.

My intuition says that Now should really be a function which does some low-level magic followed by some high-level magic and then returns a DateTime object with the correct time.

Answer 1

DateTime.Now isn't an attribute, it's a static readonly property.

Under the covers a readonly property is just a function call that returns a value, so it can do any amount of processing it wants to.

Hope this helps.

Answer 2

It's not an attribute, it's a static property on the DateTime class that looks like the following:

public static DateTime Now
{
    get
    {
        return UtcNow.ToLocalTime();
    }
}

UtcNow is another property on DateTime that returns the following:

return new DateTime((ulong) ((GetSystemTimeAsFileTime() + 
  0x701ce1722770000L) | 0x4000000000000000L));

GetSystemTimeAsFileTime is a Windows API Call.