Why is DateTime.Now a property and not a method?
After reading this blog entry : http://wekeroad.com/post/4069048840/when-should-a-method-be-a-property,
I'm wondering why Microsoft choose in C# :
DateTime aDt = DateTime.Now;
instead of
DateTime aDt = DateTime.Now();
- Best practices say : Use a method when calling the member twice in succession produces different results
- And
DateTime.Nowis perfect example of non-determistic method/property.
Do you know if there any reason for that design ?
Or if it's just a small mistake ?
I believe in CLR via C#, Jeffrey Richter mentions that DateTime.Now is a mistake.
The System.DateTime class has a readonly Now property that returns the current date and time. Each time you query this property, it will return a different value. This is a mistake, and Microsoft wishes that they could fix the class by making Now a method instead of a property.
CLR via C# 3rd Edition - Page 243
It actually is deterministic; it's output is not random, but is based on something quite predictable.
The 'current time' changes all the time; so to be relatively "the same" with each call, that value must change so that every time it's called, it's returning the current time.
EDIT:
This just occurred to me: Of course, two subsequent calls to a property getter can return different results, if something changed the property value in the interim. Properties are not supposed to be Constants.
So, that's what happening (conceptually) with DateTime.Now; its value is being changed between subsequent calls to it.
According to MSDN you should use a property when something is a logical data member of the object:
http://msdn.microsoft.com/en-us/library/bzwdh01d%28VS.71%29.aspx#cpconpropertyusageguidelinesanchor1
The go on to list out the cases where a method would be more appropriate. What is ironic is that one of the rules for a method is to use it when successive calls may return different results and of course Now certainly meets that criteria.
Personally I think this was done to eliminate the needs for the extra (), but I have found the absence of () confusing; it took me a little while to shift from the old approach in VB/VBA.