There's no direct equivalent to willSet or didSet. The closest equivalent (aside from adding code before/after your own get/set code) might be INotifyPropertyChanged [1]/INotifyPropertyChanging [2]? But they are more for external observers and add a lot of boilerplate to your code. It's possible to manage the boilerplate, however [3].

[1] https://msdn.microsoft.com/en-us/library/system.componentmod...

[2] https://msdn.microsoft.com/en-us/library/system.componentmod...

[3] https://github.com/Fody/PropertyChanged