Is SwiftUI framework declarative or imperative or neither? - swiftui

Question

I'm having a discussion with a collegue, who insists the SwiftUI is imperative. To me, it seems very declarative. Is he right?

Answer 1

As noted in numerous WWDC 2019 videos (e.g., SwiftUI Essentials and Introducing SwiftUI), SwiftUI is declarative. Apple repeatedly contrasts it to traditional, imperative approaches. The first line of their SwiftUI documentation says that it is for “declaring your app's user interface”. Apple’s SwiftUI Essentials WWDC 2019 video describes SwiftUI as their “new declarative framework.”
Admittedly, SwiftUI can be married with imperative techniques, too. For example, one can combine SwiftUI views with UIKit imperatively generated views/apps. In another example, when one adds a tap handler to a view element, one can subtly shift from the “what” of declarative programming to the “how” of imperative programming, as you outline a series of steps to be taken to achieve some task. Perhaps your colleague is alluding to one of these aspects of SwiftUI.
But it is inaccurate to contend that SwiftUI is an imperative framework. It is essentially declarative.

Answer 2

SwiftUI uses the programming paradigm known as declarative programming.
A major advantage of learning and using SwiftUI is allowing for cross-platform development for the different operating systems within the Apple ecosystem. No more having to learn four different frameworks if you want to build an app that has components on Apple Watch, Apple TV, MacBook Pro, and finally your iPhone.
It is important to know that SwiftUI does not replace UIKit. Instead, it is built on top of providing and an additional layer of abstractions for us.

Answer 3

Imperative mainly focuses on the how a program is doing something. Declarative in my mind means that SwiftUI plainly states what is going on via its syntax. In Apple's marketing blurb of SwiftUI they show a sample of code that is very declarative in my opinion. You can tell that in a view you can target a body and display images and vertically stack some text with in the body. I think its stating what is going on without low level syntax like:
#IBOutlet weak var CaptionLabel: UILabel!
#IBAction func Submit(_ sender: Any) {
CaptionLabel.text = "Hello World"
}
Based on the syntax above there is a lot of how something is working. You can see #IBAction which is declaring to the Interface builder that this is how a function is being set to a button press. To me this is kind of the how it is working not really what is happening. In the new SwiftUI behind the scenes maybe its still #IBAction and #IBOutlets but in my opinion Apple has made the syntax more declarative to humans and doesn't concern us with the behind the scenes things that are going on. I feel this way since SwiftUI is built on top of UIKit. The gauge I kind of use is if the syntax is human readable and its abstracting away a lot of the low level details of how its working then its more declarative.