Circular definition in a constant enum

Question

I'm trying to create a constant of type Enum but I get a error.. My enum is:

public enum ActivityStatus
{
    Open = 1,
    Close = 2
}

and I have a model that uses it:

public class CreateActivity
{
    public int Id;
    public const ActivityStatus ActivityStatus = ActivityStatus.Open;
}

the following error occurs:

Error 1 The evaluation of the constant value for 'Help_Desk.Models.CreateActivity.ActivityStatus' involves a circular definition...

But if I change the name of ActivityStatus property it works!

public class CreateActivity
{
    public int Id;
    public const ActivityStatus AnyOtherName = ActivityStatus.Open;
}

Why it happens?

relevant? http://stackoverflow.com/questions/211567/enum-and-property-naming-conflicts — Prof. Falken, Oct 04 '12 at 14:14
Very interesting. Note that if you remove `const` (possibly specifying `static` and/or `readonly` instead), it works! C# Language Specification section 7.6.4.1 applies in most cases, but why not in yours? — Jeppe Stig Nielsen, Feb 27 '15 at 13:23

MiMo · Accepted Answer · 2012-10-04T14:25:57.937

17

Because the c# compiler intepretes the third ActivityStatus in:

public const ActivityStatus ActivityStatus = ActivityStatus.Open;

as the name of the constant being defined instead than the name of the enumeration - hence the circular reference: you are definining a constant in terms of the constant itself.

In C# you can use the same name for members and types, and usually resolve ambiguities specifying the fully qualified names (i.e. adding the namespace), but in my experience it is not a good idea, it makes code confusing: the compiler can figure out which is which, but the poor human reading the code has an hard time figuring out if a certain name refers to a class or type or member.

edited Oct 04 '12 at 14:25

answered Oct 04 '12 at 14:12

MiMo

11,793
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2

And the solution is to change `ActivityStatus.Open` to `Namespace.ActivityStatus.Open` – Daniel Hilgarth Oct 04 '12 at 14:16
1

No, it is not a compiler bug - the problem is that third `ActivityStatus` can mean two things: the name of the enumeration or the name of the constant, the compiler has to pick one - and it picks the name of the constant (if @EricLippert shows up he can explain us why the compiler makes this choice...) – MiMo Oct 04 '12 at 14:20
1

@DanielHilgarth No, that's not the solution. Having a variable of the same name as it's type is just asking for trouble. The solution is to change the name of the variable. – Servy Oct 04 '12 at 14:28
2

@Servy, I'm not sure all agree http://stackoverflow.com/questions/211567/enum-and-property-naming-conflicts – Jodrell Oct 04 '12 at 14:32
2

@Servy: I don't agree. There more than enough samples of this. No sign of trouble. – Daniel Hilgarth Oct 04 '12 at 14:33
@murilokunze: I try to avoid it, but that's just my personal preference. It is fine to do it if you prefer - and as others pointed out above there are even example of this in the system libraries (the `System.Data.CommandType` enumeration and the `System.Data.DbCommand.CommandType` property) – MiMo Oct 04 '12 at 16:35
1

It a little curious to me that the compiler (in the parser?) decides that the third `ActivityStatus` is the constant being defined. If it were less greedy and parsed the whole statement, surely it would be valid? On the face of it, the rules are simple (probably @EricLippert would show they're not) to figure out a fallback strategy on the the assignment. Better read the spec and see what it says. In other places, the compiler can infer the expected behaviour, why not here? – nicodemus13 Nov 09 '12 at 11:25

score 1 · Answer 2 · edited Oct 04 '12 at 14:36

1

You should not create a variable with the same name of a class or enum.

Maybe it will work if you specify the namespace, like :

public class CreateActivity
{
    public int Id;
    public const TheNamespace.ActivityStatus ActivityStatus =
        TheNamespace.ActivityStatus.ActivityStatus.Open;
}

edited Oct 04 '12 at 14:36

Servy

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answered Oct 04 '12 at 14:13

Anthony Simmon

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1

you can. this problem is specific to const – Peter Porfy Oct 04 '12 at 14:15
That's not correct. You can name your variables like classes, no problem. No downvote because using the namespace on `ActivityStatus.Open` solves the compiler error. – Daniel Hilgarth Oct 04 '12 at 14:16
Well, you *can*, but you never *should*, even if there is some way to disambiguate the variable from the type when using them. – Servy Oct 04 '12 at 14:29
2

@Servy, I'm not sure all agree http://stackoverflow.com/questions/211567/enum-and-property-naming-conflicts – Jodrell Oct 04 '12 at 14:31
I disagree very strongly with this answer. Naming a variable the same as it's enum type is _extremely_ common and not a bad practice at all IMHO. – julealgon Oct 23 '18 at 21:29

Александр Киричек · Answer 3 · 2015-02-27T13:38:15.323

0

If private usage only: You can change ActivityStatus to readonly field and move setting of default value to constructor.

If public usage: You can use property with getter only.

In most of the code analyzers additional namespace will be treated as redundance in your code.

edited Feb 27 '15 at 13:38

answered Feb 27 '15 at 13:14

Александр Киричек

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score 0 · Answer 4 · answered Aug 07 '18 at 12:25

0

To avoid from the Circular Definition Problem in C#, You can reference/call the variable/type/member etc with full qualified name like

Namespace..Member/Type/ etc

Hope you will fix the error by now.

answered Aug 07 '18 at 12:25

Tahir Alvi

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Circular definition in a constant enum

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