Fine-Grained Projections have been the missing link in Reactive systems. The one thing whose absence has lead us back to the path of diffing. No Longer. 

I've been staring at this problem for months now. But it feels like the pieces are finally coming together. Join me on stream as we look again at reactivity's most elusive primitive.

Ryan Carniato

A live stream transcript exploring mutable signals and reactive state management in SolidJS 2.0. The discussion covers why mutable/nested reactivity (stores) is needed over immutable signals, comparing approaches like incremental computation (Signia), nested signal objects (as shown in a Pact article by Joy), and the tradeoffs of each. Key themes include the dangers of warping JavaScript semantics for ergonomics (critiquing Svelte runes), why signals are fundamentally functions, the observer pattern's bidirectional linking, and how fine-grained reactivity differs from React's VDOM diffing model. The stream also touches on Svelte 5's class-based runes as an indirect consequence of fighting JavaScript's composition model.

Mutable Signals Pt 2 - Solving Derivations