Question

I have an object that has several properties. If I have a pointer to one of those properties, is it possible to get a pointer to the class instance to which that ivar belongs?

for example: foo.bar, where I know the address of bar, can the address of foo be found?

This seems related to: run time references but I didn’t see any references that were quite what I’m looking for.

Thanks for your help!

Answer 1

First, you need to adjust your terminology a bit. You cannot have a pointer to a property, because a property is an interface to an object, specifying the format of the getter and setter methods.

If you had a pointer to the getter, a method (IMP) at best you could get back would be a pointer to the class, certainly you could not get back to an instance.

If you had a pointer to an ivar, I don’t believe there is any way to get back to the containing object instance. If you had an array of all posible foos, it might be possible to ask each of them for a list of ivars, and get the address of each ivar and eventuallty find the instance in question that way.

The best solution is for bar to contain a parent reference to foo, so that foo.bar.foo will give you the answer you want. But it depends on what exactly you are trying to do. The normal Cocoa way for a lot of these things is to pass foo as well, as is done for many delegates. For example:

[obj foo:foo doSomethingWithBar:foo.bar];