One thing I've found frustrating with Swift, and that we've had to deal with in libs we've built, is that there is an unavoidable boilerplate of placing an `[unowned self]` at the top of your callbacks (e.g. `map` in the linked framework), or else you introduce a reference cycle.

If you forget this `[unowned self]`, which is very easy to do, everything compiles fine and now you have a subtle memory issue to track down. I wish there was a language construct to allow you to define closures that have every captured variable unowned (or weak) by default.

I would, at the very least, emphasize somewhere in your docs with big bold letters how important it is to add the boilerplate, or users of Bond will definitely get bitten by this.