Page 130 : we have

this instruction is instantiating a DateTime object and initializating it via
the default constructor , right ?
And myTime is a reference to this particular object.
But in the second line we have

DateTime.Now is a property but also an object itself
and this is really confusing me : now myTime is a reference to another
object ? And if so , what happened to the first object ?


Thanks a lot for any explanation !

There are no objects involved at all, only values. Objects are instances of reference types. DateTime is a value type.

DateTime myTime = new DateTime();

loads the address of the local variable "myTime" onto the evaluation stack and initializes the value stored at that address to a DateTime struct whose fields are initialized to default values. The struct's static constructor is called.

myTime = DateTime.Now ;

pops the return value of the Now property off the top of the evaluation stack and stores it at the address of "myTime", overwriting the initial default values. "myTime" is just an alias for the address on the stack. Its value isn't a reference to any object on the heap. It's value is the struct itself. Assigning the return value of Now to that address simply overwrites any value already stored at that address.

You could just do:

DateTime myTime = DateTime.Now;

Thanks for your kindness , Bob.
I was suspecting that the situation was a bit tricky
and at least now i'm SURE it is !

OOP concepts aren't really easy to grasp at the beginning .
However , your explanation is very clear.

Best regards

Piero ( pepitagold )

Hi Piero,

Yup, its tricky. Just stay on it.

Here's a couple of links you might find helpful that cover how reference types and values types get stored in managed memory. The Jon Skeet piece is a bit of a "classic".

http://www.yoda.arachsys.com/csharp/memory.html
http://www.c-sharpcorner.com/UploadF...rp_memory.aspx

HTH,

Bob

Bob's correct in the way things get allocated on the stack. Also, if all you want is the current date and time, you don't even need to create myTime, just use the Now property.

__________________
Jack Purdum, Ph.D.
Author: Beginning C# 3.0: Introduction to Object Oriented Programming (and 14 other programming texts)