public static (const) in a generic .NET class

Question

Is there a syntax trick to get to the constant in a generic class without specifying an (ad-hoc) type?

public class MyClass<T>{
    public const string MyConstant = "fortytwo";
}

// I try to avoid this type specification.
var doeswork = MyClass<object>.MyConstant;  

// Syntax similar to what I'd like to accomplish.
var doesnotwork = MyClass.MyConstant;

There is a caveat about the static variable (constant) not being shared between different types like MyClass<object> and MyClass<int> but my question is about possible available syntax trick.

You could create a non-generic class `MyClass` for the constant. — Dirk, Jan 08 '15 at 14:07
WARNING: Using `const` in public classes can cause headaches **if** the assembly is going to be referenced in another program or assembly. Use `readonly` instead. — B0Andrew, Jan 08 '15 at 14:35
Here's a [reference](http://www.stum.de/2009/01/14/const-strings-a-very-convenient-way-to-shoot-yourself-in-the-foot/) for @B0Andrew's warning — stuartd, Jan 08 '15 at 16:41

Oblivious Sage · Accepted Answer · 2015-01-08T16:23:56.223

16

Use a non-generic abstract parent class.

public abstract class MyClass
{
   public const string MyConstant = "fortytwo";
}

public class MyClass<T> : MyClass
{
   // stuff
}

var doeswork = MyClass.MyConstant;

That of course assumes that there's some reason the constant needs to be part of the generic class; if it has public accessibility, I'm not seeing a reason why you wouldn't just put it in a separate class.

Having a non-generic abstract parent class is a good idea for every generic class you make; the generic class is actually a template for the specific subtype classes, rather than a true parent, so having a true non-generic parent can make some techniques (such as, but certainly not limited to, this one) a lot easier.

edited Jan 08 '15 at 16:23

answered Jan 08 '15 at 14:08

Oblivious Sage

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The reason I checked this as answer was that it was very short (=readable) and solved My Problem. Kudos to @MatthewWatson for effort and time spent. – LosManos Jan 08 '15 at 14:20
Your class names are inconsistent. – Rawling Jan 08 '15 at 14:31
@Rawling In what sense? – Oblivious Sage Jan 08 '15 at 14:34
1

`MyClass.MyConstant` won't compile as there is no `MyClass` class. – Rawling Jan 08 '15 at 15:24
1

@Rawling Fixed. Someone else edited in the `doeswork` line that had the problem, but I approved the edit without looking as closely as I should have, so that's on me. – Oblivious Sage Jan 08 '15 at 16:26
1

Sadly, this solution does not work anymore if your class extends another generic base class and you need to pass on T to your base class. – Felix K. Jun 06 '18 at 09:33

score 6 · Answer 2 · answered Jan 08 '15 at 14:08

Something like this works:

using System;

namespace Demo
{
    public class MyClass // Use a non-generic base class for the non-generic bits.
    {
        public const string MyConstant = "fortytwo";

        public static string MyString()
        {
            return MyConstant;
        }
    }

    public class MyClass<T>: MyClass // Derive the generic class
    {                                // from the non-generic one.
        public void Test(T item)
        {
            Console.WriteLine(MyConstant);
            Console.WriteLine(item);
        }
    }

    public static class Program
    {
        private static void Main()
        {
            Console.WriteLine(MyClass.MyConstant);
            Console.WriteLine(MyClass.MyString());
        }
    }
}

This approach works for any static types or values that you want to provide which do not depend on the type parameter. It also works with static methods too.

(Note: If you don't want anybody to instantiate the base class, make it abstract.)

public static (const) in a generic .NET class

2 Answers2

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