MVVM, architecture having 3 components Model, view and View model, Model- handles all data related things, data is stored in model View- responsible for UI View Model- acts as a intermediary b/w model and view when we are interacting with View , then Model response to these change, update the model and viewModel listens to this changes nd then view is updated with the updated data, All logic related things and all code i.e different from Controller will be written in viewModel, Easy reusable,testable Struct vs Class- struct values types, immutable, does not support inheritance, struct gives default init but not having denit,m/m management is efficient,== equality operator to match the contents of all properties Class reference types, mutable,support inheritance, having init and deinit, m/m management is done using ARC, === operator to match the reference point for both instance FlatMap vs Compact Map- both are higher order functions used to transforms collection flatmap used to transform 2d array into single array or flatten the array of array into an array. Does not remove nil values Compact map- used to transform element of collection by applying the provided closure and by removing nil values.