Ari Grant, an iOS Engineering Manager at Facebook, will explore how Facebook’s approach to redesigning the data layer of the app was followed by a rewrite of News Feed in the iOS app using similar functional design techniques to build a reactive UI layer with immutable objects, internal view reuse, and all view-configuration performed by the strongly instrumented, private infrastructure. He will describe the view system his team built and how they managed to reduce the code behind Feed by nearly 70%. Ari will end by describing how the team rewrote all of feed one piece at a time, all while keeping the system up and running and how these efforts have led to an even larger focus on speed and performance.