Re: Dynamic enums

Eric Sosman <esosman@ieee-dot-org.invalid>
Tue, 11 Oct 2011 22:05:40 -0400
On 10/11/2011 9:34 PM, Linus Flustillbe wrote:

Let's say I have an ENUM defined as

public enum xxx {
   A, B, C, D, E

Now here's my question.
Let's say I have a table called foobar which has the following rows

A 1
B 2
C 3
D 4
E 5

My code is written and is working great. The enum xxx is used as a
lookup on the foobar table. If I add a row to foobar like

F 6

I need to add another enum to the xxx enum and rebuild my project.

So my question is, is there something like a dynamic enun: by this
could I call a method on the xxx enum like

xxx.addnew("F") that would make F a valid enum of xxx and not have to
rebuild my project?

     No. The names of enum constants are compile-time artifacts,
just like the names of local variables. At run-time, all such
things have disappeared (well, they may survive in ancillary debug
data, but the C language has no access to such things).

     Besides, what use could you make of such a dynamic enum, even
if you could create it? If there's a `switch' with cases for
A,B,C,D,E, it won't magically acquire a new case for F. If you've
got an array of the values A,B,C,D,E that you traverse from time to
time, the array won't magically lengthen and acquire an F-valued
element. What do you expect to be able to do with F, given that the
code as written never mentions the identifier `F' at all? (Worse,
what do you expect to do if the code *does* use `F', but in some
completely different context? Does creating the dynamic enum `F'
cause a retroactive compilation failure?)

Eric Sosman

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