Question

I understand that Properties in Objective-C allows us to compactly define:

1. setter
2. getter
3. data

I would like to use Properties, but it would be nice if I could decouple the data from the getter/setter.

In other words, I like the getter/setter interface of Properties, but I would like to define my own internal representation of data.

For instance, if I were to define MyOwnTime class, I want getters/setters for Properties like hour, date, and minute (as a consumer, I want to be able to set them and get them). However, to save memory in the representation, rather than store date, month, year, hour, minute, second, etc…, I prefer to store secondsSinceEpoch as an unsigned long.

In my situation should I/can I use Properties? How would I do this? Or should I manually roll my own setters and getters?

Answer 1

You can certainly do this. Indeed, it’s pretty common. Since the mapping to data is not direct, you cannot synthesise the methods, you have to write the getters and setters manually. But the property will work like any other.

As a simple dummy example:

@interface BytePair
{
    UInt16 data;
}

@property UInt8 loByte;
@property UInt8 hiByte;
@end

@implementation BytePair

- (UInt8) loByte
{
    return (UInt8) data & 0xff;
}

- (void) setLoByte:(UInt8)lo
{
    data = (data & 0xff00) | lo;
}

- (UInt8) hiByte
{
    return (UInt8) (data & 0xff00) >> 8;
}

- (void) setHiByte:(UInt8)lo
{
    data = (data & 0xff) | (lo << 8);
}

@end

Or whatever. You get the idea.