Alternatively, a dictionary mapping keys onto blocks of type (void(^)(void)),
which each compute their result. That, combined with typedef
void(^voidBlock)(void); voidBlock constant(id r) { return [^{return r;} copy];
} would give you a dictionary that can store both constants and computed values.
Bob
On 17 May 2013, at 12:07, Sandor Szatmari <admin.szatmari....@gmail.com> wrote:
> If you go the dictionary route a simple category on NSDictionary would allow
> you to compute dynamic properties such as area = length * width.
>
> Sandor Szatmari
>
> On May 17, 2013, at 1:43, Trygve Inda <cocoa...@xericdesign.com> wrote:
>
>> I need to keep a small (few thousand) record database of sorts. Each record
>> has some pre-detertermined fields, but the user can add there own fields to
>> to a limited extent. It is a pretty light use so CoreData isn't what I
>> really want, plus migrating to future structures is an issue with CoreData.
>>
>> This will be simple objects in an NSMutableArray.
>>
>> I can use an array of NSMutableDictionaries or perhaps an array of
>> class-based custom cocoa objects.
>>
>> One nice thing about the object route is that I can have some fields
>> (properties) be based on a calculation rather than real storage like they'd
>> be in an NSMutableDictionary.
>>
>> E.g.
>>
>> NSNumber length
>> NSNumber width
>> NSNumber area
>>
>> In an object area could be a method returning length*width instead of an
>> instance var for area.
>>
>> The trouble comes in the fact that I need to be able to add properties at
>> runtime. For the dictionary option, it is easy - just make sure the key
>> names don't collide and I can add more keys to each dictionary.
>>
>> But for the objects I don't see a nice way to do this
>>
>> There is setValue:forUndefinedKey: and then each object could keep a local
>> dictionary of these "defined at runtime" keys.
>>
>> Thoughts on this?
>>
>>
>>
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