A port of DynamicData for FerroUI: reactive collections, change sets, observable caches and lists with their operators, independent of the user interface
//! `IKey<T>` (`Cache/IKey.cs`).
/// An object that knows its key (`IKey<out T>`): `StartWithItem(item)` and the groups read it.
pubtraitIKey<K> {/// The key (`Key`).
fnkey(&self)-> K;}