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Why Can't I Have "public static const string S = "STUFF"; In My Class

Answer 1

+22 A:

const implies static.

Joel Coehoorn 2009-01-02 22:37:34

Is there a 'final' like modifier? Would that be readonly?

jjnguy 2009-01-02 22:39:03

const makes the variable constant and cannot be changed.

Samuel 2009-01-02 22:39:51

@jinguy: const inherently means static -- if you have any const, it's already static, and static therefore does not need to be nor cannot be specified.

John Rudy 2009-01-02 22:40:50

I don't think C# has a direct analog to "final"

Joel Coehoorn 2009-01-02 22:41:48

The only equivalent would be readonly, but it's not quite the same.

Lasse V. Karlsen 2009-01-02 22:42:33

... at least in this context, I should add. You can mark a class 'sealed' to prevent inheritance.

Joel Coehoorn 2009-01-02 22:42:58

The more C# I write, the more I realize I'm a Java fanboi.

jjnguy 2009-01-02 22:43:31

@jjnguy: Why? readonly is actually more flexible than Java's final for variables - you can set it as many times as you like in the constructor, but not elsewhere. That can be very handy.

Jon Skeet 2009-01-02 23:01:44

And "const" implies "readonly" as well as static, btw.

Jon Skeet 2009-01-02 23:02:22

Consts are inlined at compile time and are not present in the static type object at runtime. Statics aren't inlined and live inside the type object. I add this just because nobody's mentioned the difference...

Will 2009-01-02 23:07:22

They're still present at execution time - you can get at them with reflection, for example (with GetField).

Jon Skeet 2009-01-02 23:16:13

Jon, please make the next C# allows const static readonly all on one and that they don't come up with this "foo implies bar so foo bar is invalid" stuff. it annoyed me all day long when i programmed with c# in school

Johannes Schaub - litb 2009-01-02 23:32:46

@litb: Wow, I wish I had that sort of influence ;) I wouldn't use it for that though - I have no problem with disallowing redundancy. (It's like putting "public" on interface members. Ugh.) There are plenty of more important things to change in C#. Readonly autoproperties would be my first choice...

Jon Skeet 2009-01-03 00:02:50

I don't hate C# I guess...I'll just use readonly I guess.....thanks for all of the good info!

jjnguy 2009-01-03 15:02:09

Answer 2

+15 A:

From the C# language specification (PDF page 287 - or 300th page of the PDF):

Even though constants are considered static members, a constant declaration neither requires nor allows a static modifier.

splattne 2009-01-02 22:40:21

Also available here: http://msdn.microsoft.com/en-us/library/aa645749(VS.71).aspx

Lasse V. Karlsen 2009-01-02 22:47:04

Answer 3

+2 A:

A const member is considered static by the compiler, as well as implying constant value semantics, which means references to the constant might be compiled into the using code as the value of the constant member, instead of a reference to the member.

In other words, a const member containing the value 10, might get compiled into code that uses it as the number 10, instead of a reference to the const member.

This is different from a static readonly field, which will always be compiled as a reference to the field.

Note, this is pre-JIT. When the JIT'ter comes into play, it might compile both these into the target code as values.

Lasse V. Karlsen 2009-01-02 22:41:47

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Why Can't I Have "public static const string S = "STUFF"; In My Class

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