How to concisely handle words that don't have an antonym
Ignoring the legality of the words and using "unwrapper" is a possibility
English is a changing language. Your goal is to communicate precisely with humans. Given that "unwrap" and "wrapper" are familiar words, no English reader will have trouble understanding what an "unwrapper" is, and is what I would use.
but spellcheck is going to complain
Our software should serve us, and not vice versa.
I need words to name "the thing that undoes".
Looking at this from the software architecture, if you find yourself needing to define a pair of names for each action, it seems like you're begging for a better abstraction. One option is to bundle the doing and undoing behavior into a single actor for each action. It's common for classes implementing the Command pattern to do that. If not that, maybe you can make a single "undoer" type that can generically undo any action.
Software has spawned many new words and new uses of old words, so I think you can get inventive. If there's no easy antonym for "wrapper," start paring suffixes. That gets you to "wrap" in this case, the antonym of which is "unwrap." Hence, I suggest you go with "unwrapper," and simply add it to your spelling dictionary. The meaning of "unwrapper" should be instantly obvious to your users/readers, which is largely your goal.
Instead of using nouns, use verbs. That way, for the instance with wrapper, you can use undo or unwrap, the spell check won't have a problem, and you'll know what it is.
Think a little more about the principles you're dealing with. You're not necessarily looking for "antonyms", just for other roles in a process.
In the case of your wrapping example, the wrapper you describe is probably responsible for wrapping content up in some container. Logically, something else will eventually want to remove that content from the container. Such a thing could be called:
- An opener, especially if you want to emphasize its job as something which knows how to operate the container to open it
- An exposer, especially if you want to emphasize its job as something which makes contained content accessible outside of its container
- An extractor, especially if you want to emphasize its job as something whcih removes content from containers
I wouldn't call any of these things "antonyms" to wrapper, but based on my understanding of your requirements I'd say these are all appropriate terms to your particular example.
The problem seems to lie in the fact that in non-technical English, a "wrapper" is a thing, not a process. (Ref: http://www.oxforddictionaries.com/definition/english/wrapper.) You are looking for nouns to represent "the processes of wrapping and unwrapping a collection of things".
The gerunds "a wrapping" and "an unwrapping" might work, though that usage doesn't agree with the dictionary definition of "a wrapping" as a synonym of "a wrapper". At least they will get through your spelling checker, unless its grammar parsing is too clever for its own good.