Introduction to DHDeclarable

• At its core, DHDeclarable is a protocol and a function
• Starting with the protocol: protocol DHDeclarable
• The protocol requires that you implement a method: declaredWith
• The protocol implements it for you:

@discardableResult func declaredWith(_ then: (_ instance: Self) -> Void) -> Self {
    then(self)
    return self
}

• This function does two things: 1) return self and 2) call a closure, with self as the parameter.
• Using this method, it allows you to initialize objects and mutate properties with syntactic sugar.
• Note: @discardableResult silences a warning if the return object is not used.

Not using DHDeclarable

let stackView = UIStackView()
stackView.axis = .vertical
stackView.distribution = .fill
stackView.spacing = 10
stackView.addArrangedSubview(...)
stackView.addArrangedSubview(...)
stackView.addArrangedSubview(...)
return stackView

Using DHDeclarable

return UIStackView().declaredWith {​​​​​​​​​​​​​​​​​​​​​​​​​ stack in
    stack.axis = .vertical
    stack.distribution = .fill
    stack.spacing = 10
    stack.addArrangedSubview(...)
    stack.addArrangedSubview(...)
    stack.addArrangedSubview(...)
}

Notes:

• We’re using the return value of with and the closure parameter, self, that declaredWith provides
  • The initializer of UIStackView() is called first
  • After the stack view is initialized, declaredWith is called
  • The properties of the stack view are updated
  • Finally, the stack view with the updated properties is returned.
• Note that this is not asynchronous, the closure is called before the return.

Why use DHDeclarable?

• This allows for more declarative code
• Accessibility: using hierarchical view code, views can be made to automatically scale and text to resize.
• Views can be expressed with a hierarchy, or with more clear state properties
• This makes writing programatic UIKit code a little easier than a traditional “linear” approach.
• DHDeclarable was designed to help bridge the gap between Storyboards, programatic UIKit, and SwiftUI
• When using DHDeclarable with UIKit objects, all code can be converted to traditional programatic code, it does not seek to replace UIKit in any way. It builds upon it.
• DHDeclarable is more of a design principle, extension of UIKit, and at it’s core it is one function: declaredWith

Continue learning about DHDeclarable in the next article: Building on the Basics, or view the map.