Why is DateTime a structure in .Net?

Question

Why is DateTime a structure instead of an inheritable class?

(I would like to be able to override the ToString() method but I can't.)

Answer 1

Probably because it was seen as a small, simple and immutable data structure, much like an integer or decimal. Making it a struct under these conditions make using a DateTime very efficient. If it had been made a class, this efficiency benefit would have been lost because that would require memory allocations every time you create a new DateTime.

Besides, how many variant forms of a DateTime can you come up with? (Ignoring the allternate ToString implementations you have in mind.) It's not exactly a type that invites polymorphism.

Note that for using a different formatting strategy for your DateTimes, as I think you want, you'd better look at a different way to format than just using ToString. If you look at the ICustomFormatter interface in MSDN, you'll see how you can plug into the String.Format pipeline to override formatting without needing to subset an existing type.

Answer 2

You can use Extension Methods for this: Declare extension:

public static class DateTimeExtensions
{
    public static string ToStringFormatted(this DateTime date)
    {
        return date.ToString("{d}");
    }
}

Use extension:

using DateTimeExtensions;
...
var d = new DateTime();
System.Diagnostics.Debug.WriteLine(d.ToStringFormatted());

This way you can simple implement your own method thats used on DateTime. This way it can easily be used everywhere within you solution. Only thing you have to do is using the namespace.

Ref: Extension Methods (c#)