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Coral Doe
Coral Doe

Reputation: 1941

It is proper to have an enum with a single value?

This is kind of a very simple question, but I'm really interested to know what is the good practice.

I have an system including a logging sub-system. Logs contain informations about users ID. The logging simplified is like this:

log.RegisterEvent(eventType, userID, eventDetails);

Some events are system events and they have not associated an userID. As the user IDs are positive integers, I consider that 0 means that the event doesn't reffer to a user:

log.RegisterEvent(eventType, 0, eventDetails);

But putting 0 there is just... not right. I thought of using enums, like:

enum UserID
{
    None = 0
}

But is it ok to have an enum with only one value? It is better to use a static constant? Or it is anothe better way?

Upvotes: 6

Views: 7480

Answers (5)

Jeppe Stig Nielsen
Jeppe Stig Nielsen

Reputation: 61952

I don't like your enum because most developers will not expect that (UserIDEnum)42 is used, since it's not a "defined" value of the enum type.

Also the idea of a "magic" constant is not very appealing to me.

This seems an obvious case for a nullable type, namely int? (also called Nullable<int>). Most developers will understand that if the int? is null (HasValue is false) it means absence of a user ID, and if it's 42, then that's the user ID.

So change the second parameter to type int?. and calls will look like this:

log.RegisterEvent(eventType, null, eventDetails);    // no user ID in this case
log.RegisterEvent(eventType, userID, eventDetails);  // variable userID is automatically "lifted" from int to Nullable<int>

Upvotes: 3

Justin Harvey
Justin Harvey

Reputation: 14672

Change the logging sub-system to define an overload that takes no user id.

In that overload you could just code a 0 as it is now the only place it will be used.

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1500865

"User ID" doesn't sound like a natural kind of enum to me. It's not like there's a natural bounded set of users globally.

A constant value would make more sense:

const long UnknownUserId = 0;

There are cases where an enum with a single value would make sense, but it would almost always be for future expansoin.

Upvotes: 8

Martin Liversage
Martin Liversage

Reputation: 106836

It is better to use a constant - otherwise you would have to cast the enum value when used because the API really expects a number. Enums are for closed sets of values and user ID's do not belong to this category.

Upvotes: 5

Nikhil Agrawal
Nikhil Agrawal

Reputation: 48568

Yes what use is an enum when there is no diversity in there.

Upvotes: 0

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