The hot-swap capability isn't something specific to Eclipse, its built into the JVM. Its also pretty limited, you can only change method bodies, you can't add methods, classes, class variables, and often things like annotation changes aren't picked up. Eclipse, IntelliJ, etc all use this. There is JRebel which is a custom implementation that allows much more robust code injection, but its not free.
Hotswap is great for tweaking values/logic after you've nailed down your method flow but it can have negative effects as well which aren't immediately apparent. I've seen a few hunks of code end up overly complicated as the developer hit a point where they really needed to break the code into more methods but didn't since you can't Hotswap in new methods and they didn't want to wait for the app to restart.
I don't really know how you would do this with Objective-C as its compiling to machine instructions. It would be very tricky as you don't have the luxury of a VM that explicitly supports it running your code.
Objective-C supports code replacement very well as it "run-time binds" selectors to method implementations. By injecting a bundle with a new implementation in a category it takes precedence over the original implementation as if the method had been "swizzled". The previous implementation linked into the app is taken out of play and ignored. This is all looked after by the application I mentioned. The complications seem to be minimal in my experience as long as you don't change the class interface...
Hotswap is great for tweaking values/logic after you've nailed down your method flow but it can have negative effects as well which aren't immediately apparent. I've seen a few hunks of code end up overly complicated as the developer hit a point where they really needed to break the code into more methods but didn't since you can't Hotswap in new methods and they didn't want to wait for the app to restart.
I don't really know how you would do this with Objective-C as its compiling to machine instructions. It would be very tricky as you don't have the luxury of a VM that explicitly supports it running your code.