I've been using thrift on a decent variety of iOS projects for the last ~4 years. Every time I set a new project up, I invariably end up inventing some way to invoke thrift RPC calls via Objective-C block syntax. I usually end up ripping apart the generated classes by declaring their private methods, and then writing a bunch of boilerplate all so that I can avoid using the provided HTTP client, which makes synchronous requests.
This is a decent stab at letting the generator take care of this problem for me, and everyone else. It ended up being pretty heavy handed with t_cocoa_generator.cc, but I've spent a while testing this and am pretty confident I managed to avoid breaking anything. I realize this is a large change, so I've put up the sandbox I was using to test on github if that makes it easier to review. If you want the tl;dr; about what practical changes this has on generated sources:
I'd welcome feedback or proposed modifications if this approach isn't quite right.