How to declare a class instance as a constant in C#?

Question

I need to implement this:

static class MyStaticClass {     public const TimeSpan theTime = new TimeSpan(13, 0, 0);     public static bool IsTooLate(DateTime dt)     {         return dt.TimeOfDay >= theTime;     } } 

theTime is a constant (seriously :-), like π is, in my case it'd be pointless to read it from settings, for example. And I'd like it to be initialized once and never changed.

But C# doesn't seem to allow a constant to be initialized by a function (which a constructor is). How to overcome this?

Answer 1

Using readonly instead of const can be initialized and not modified after that. Is that what you're looking for?

Code example:

static class MyStaticClass {     static readonly TimeSpan theTime;      static MyStaticClass()     {         theTime = new TimeSpan(13, 0, 0);     } } 

Answer 2

Constants have to be compile time constant, and the compiler can't evaluate your constructor at compile time. Use readonly and a static constructor.

static class MyStaticClass {   static MyStaticClass()   {      theTime = new TimeSpan(13, 0, 0);   }    public static readonly TimeSpan theTime;   public static bool IsTooLate(DateTime dt)   {     return dt.TimeOfDay >= theTime;   } } 

In general I prefer to initialise in the constructor rather than by direct assignment as you have control over the order of initialisation.