Working an enum

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K Viltersten - 19 Mar 2008 05:56 GMT

I've create a class Clock for entering
handling directions. It has twelve
values, 0 through 11, and methods for
jumping back and fort in time.

As it's now, i use a method for
controlling the pass over midnight.

void doJumpAhead ()
{
this.time++;
if (this.time > 11)
this.time = 0;
}

It just stroke me that i should be
able to use enum type. However, i've
seen no info on how to make

enum Direction : byte
{
One, Two, ... Twelve
}

to a circular entity. I believe, the
way it's shown above, it'll only keep
on increasing if i use "++" on it. Is
there a work-around?

--
Regards
Konrad Viltersten
--------------------------------
sleep - a substitute for coffee for the poor
ambition - lack of sense to be lazy

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Gilles Kohl [MVP] - 19 Mar 2008 07:42 GMT

>I've create a class Clock for entering
>handling directions. It has twelve
[quoted text clipped - 10 lines]
> this.time = 0;
> }

You could use the modulus operator "%":

time = (time + 1) %12;

(would save the if statement)

>It just stroke me that i should be
>able to use enum type. However, i've
[quoted text clipped - 9 lines]
>on increasing if i use "++" on it. Is
>there a work-around?

You could again use %, but as you can't use it on enums directly, some casting
is required, e.g.

time = (Direction)(((int)time + 1) % 12);

Regards,
Gilles.

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K Viltersten - 19 Mar 2008 08:11 GMT

>>I've create a class Clock for entering
>>handling directions. It has twelve
[quoted text clipped - 36 lines]
>
> time = (Direction)(((int)time + 1) % 12);

Yes, but i was looking for a sytax to
define the struct in such a way that the
"warping" is "already there".

Plus, i try to avoid modulo as plague due to
performance resons.

--
Regards
Konrad Viltersten
--------------------------------
sleep - a substitute for coffee for the poor
ambition - lack of sense to be lazy

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Peter Duniho - 19 Mar 2008 08:42 GMT

> Yes, but i was looking for a sytax to
> define the struct in such a way that the
> "warping" is "already there".

I don't really get the question. Is it a requirement that you use the
++ syntax? If so, then you can't do what you are asking, not without
special code like you and Gilles have posted. Enums in C# are really
little more than a wrapper around some integral type other than char, and
so they pretty much only do the things you could do with an integral type.

If you can use alternative syntax, I suppose one solution would be to
provide a mapping array:

Direction[] dirNext = { Two, Three, Four, Five, Six, Seven
Seven, Eight, Nine, Ten, Eleven, Twelve, One };

Then the next Direction is just:

Direction dirCur = Direction.One;

dirCur = dirNext[(int)dirCur];

(I'm sitting here wondering if extension methods word on enums...if so,
you could even make an extension method so that the code actually looked
something like: "dirCur = dirCur.Next()", putting the mapping array lookup
into the "Next()" extension method)

> Plus, i try to avoid modulo as plague due to
> performance resons.

Now _that_ I think isn't sensible. I doubt that modulo is all that
expensive anyway as compared to the conditional (it certainly has the
advantage of avoiding branching, so there's no branch-prediction to go
wrong), and even if it were, your code would have to be doing basically
_only_ modulo for that to be a concern.

Pete

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Working an enum

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