https://forums.swift.org/t/dynamicviewproperty/25627/7
So this is my implementation: https://github.com/swiftwebui/SwiftWebUI/blob/master/Sources/SwiftWebUI/Properties/DynamicViewProperty.swift#L9 11
I'm using Reflection (the lib) to find the offset positions of the properties in the View.
To make the View's value "mutable" one just casts the pointer to a mutable one. Which explains why this works even if the properties are defined as let. Not sure whether that is really sound (optimiser might layout the properties differently?), but I guess the layout should be stable as part of the "ABI".