From: Pit Capitain <pit@...>
Date: 2005-08-03T01:35:52+09:00
Subject: Re: enum collection of constant values

Jim Menard schrieb:
> Garance A Drosehn wrote:
> 
>> I'd like to have a set of constants for a class, where their values
>> need to be unique, and preferably compact.  For instance:
>>    SB_NONE = 0; SB_GOOD = 1; SB_BAD = 2; SB_LOGIC_ERR = 3;
>>    SB_MAX = SB_LOGIC_ERR
>>
>> but if I want to modify this list by adding something in the middle,
>> then I have to remember to increment (by hand) all the values
>> which come after that new value.
>>
>> In C, I would do something like:
>>     typedef enum { SB_NONE, SB_GOOD, SB_BAD,
>>         SB_LOGICERR } sb_set;
>>
>> Looking through the pickaxe book, it looks like the closest thing
>> I can do is to create an array of words, and then use the indexes
>> of where those words are in the array.  But that isn't really the
>> same thing.   I'd like the efficiency of having constant values,
>> which would be referred to by name.
>>
>> (And after I have that for a compact set of values, I'd want a
>> similar feature which would give me a bit-wise unique set of
>> values.  Eg:  SB_MODA = 1; SB_MODB = 2; SB_MODC = 4;
>> SB_MODD = 8; -- such that I could combine the values together
>> using '|', and tell which values were 'or'-ed together to get that
>> combined value...)
> 
> Use symbols. They are similar to strings, but every use of the same 
> symbol uses the same value, and they are very compact.
> 
> state = :none
> state = :good if all_is_well
> # ...
> state = :logic_error

... and for a set of values use the class Set.

Regards,
Pit