Filmed at https://2018.dotswift.io on January 29th in Paris. More talks on https://dotconferences.com/talks How can we define some data type (for example a view layout) such that (1) we can later add new variants (new views) and (2) we can add new behavior (rendering to AppKit in addition to UIKit) without losing type safety or touching the first bit of code? This is known as the Expression Problem. Will Brandon find a way to solve it?