UIs Are Not Pure Functions of the Model – React.js and Cocoa Side by Side (2018)

Of course, they could have just used Cappuccino, but "details". Some more details were that their version of drawRect: was called render() and returned HTML instead of drawing into a graphics context, but that's just the reality of living inside a browser. And of course there was react-canvas.

Overall, though, the use of a true MVC UI framework seemed like a great step forward compared to directly manipulating the DOM on user input, at least for actual applications.

Imagine my surprise when I learned about React.native! It looked like they took what I had assumed to be an implementation detail as the main feature. Looking a little more closely confirmed my suspicions.

Fortunately, the React.js team was so kind as to put their basic ideas in writing: React - Basic Theoretical Concepts (also discussed on HN) ). So I had a look and after a bit of reading decided it would be useful to do a side-by-side comparison with equivalents of those concepts in Cocoa as far as I understand them.

The core premise for React is that UIs are simply a projection of data into a different form of data. The same input gives the same output. A simple pure function.

We do not make the (unwarranted) assumption that this transformation can or should be expressed as a pure function. While that would be nice, there are many reasons why this is not a good idea, some pretty obvious.

You can't fit a complex UI in a single function though. It is important that UIs can be abstracted into reusable pieces that don't leak their implementation details. Such as calling one function from another.

Fortunately we have such reusable pieces, they are called objects, and we can group them into classes. Following the MVC naming conventions, we call objects that represent UI views, in Cocoa they are instance of NSView or its subclasses, in CocoaTouch the common superclass in called UIView.

To achieve truly reusable features, it is not enough to simply reuse leaves and build new containers for t

Source: HackerNews (https://news.ycombinator.com/item?id=45704216)