Back when Booking.com was still a fast-growing travel website with more web users than those using the app, I was the second iOS developer in the team. I also contributed to the brand new Booking Tonight app, with my most promiment contribution being the time zone support for same night bookings.
This project involved thorough usage of MapKit for searching and fine-tuning hotels on a map by location. As the app was a universal binary, all the new functionality had to be adaptive.
Being a data-driven company that relies heavily on A/B testing to make product development decisions, I learned a lot about experimentation on iOS using custom frameworks to turn on and off features by remote switches as well as provide alternative implementations to the end-users.
The project involved a lot of coordination with the API team to build RESTful endpoints. In the end, I learned a lot bout scalability and experimentally validating various hypotheses.