Reconciling properties of structs and DateTime

Question

I have been looking through the DateTime structure and I am slightly confused.

My understanding with structs is that you cannot assign \'default values\' of fields. If t

Answer 1

Jon Skeet is right it's all about the difference between fields and other members. One could really make a "date time" like this:

struct MyDateTime
{
  // This is the only instance field of my struct
  // Ticks gives the number of small time units since January 1, 0001, so if Ticks is 0UL, the date will be just that
  readonly ulong Ticks;

  // here goes a lot of instance constructors,
  // get-only instance properties to show (components of) the DateTime in a nice way,
  // static helper methods,
  // and lots of other stuff, but no more instance fields
  ...
}

So in reality, MyDateTime is just a wrapped ulong with an interpretation, and a lot of nice ways to show and manipulate that ulong.

Answer 2

You need to understand the difference between fields and properties.

The fields are all initialized to 0, but the properties can do what they like with those fields. Sample:

public struct Foo
{
    private readonly int value;

    public Foo(int value)
    {
        this.value = value;
    }

    public int ValuePlusOne { get { return value + 1; } }
}

...

Foo foo = new Foo(); // Look ma, no value! (Defaults to 0)
int x = foo.ValuePlusOne; // x is now 1

Now obviously DateTime is a smidge more complicated than this, but it gives the right idea :) Imagine what "A DateTime with the field explicitly set to 0" would mean... the "default" DateTime just means exactly the same thing.