> In casual conversation I've had it actually isn't that high, despite it being one of the central promises of RN.
But applications written in React Native aren't cross platform, are they? You have different components depending on the platform. My understanding is that they claimed you wouldn't have to learn a different framework when switching to a new platform, not that your apps would be portable.
Applications written in React Native typically are cross-platform; saying that they are not is a pretty large misrepresentation of the framework.
At its base React Native provides a common set of native components with the same API on both iOS and Android such as View, Image & Text which can all be styled and laid out through common APIs. These APIs pretty much give you most of what you need to make an entire APP. Sometimes you may want to have different behavior per platfrom and for that you can use the Platform API (provided by React Native) to switch for each platform. This would allow you to do things like change the styling on each platform or the native components you use.
React Native makes it pretty easy to expose native components to JavaScript. It is also up to the native component author if they want to create a common API for all platforms that they support. In the case of Views & styling it makes a lot of sense to have the same API on iOS and Android, but sometimes they are some platform features that are only available on one platform.
Wile Swift Layout is not cross-platform, it may soon be and I think it does a lot for promoting declarative UI & maybe they did take some inspiration from React!
They are. If you make a react native project using the official boilerplate generator, the resulting project will be able to run on both Android and iOS out of the box, with no modifications. It's true that you might need to use native APIs and components for specific features, but the everyday UI building blocks of RN are cross platform. These are(in my mind): the flexbox layout engine, styleable box/image/text components, animation system, and a touch and gesture interaction system. In addition many of the other parts are cross platform too: geolocation, device dimensions, activity indicators, alerts etc.
Even some of the built-in components are platform specific though, such as the segmented control for iOS and view pager for Android. But the nice thing is you don't need to create a separate project to use these, you can just chose the appropriate one at runtime based on the platform.
But applications written in React Native aren't cross platform, are they? You have different components depending on the platform. My understanding is that they claimed you wouldn't have to learn a different framework when switching to a new platform, not that your apps would be portable.