SlashConfig

SlashConfig provides a convenient way to mutate value properties and return a mutated copy. Here is a small usage example:

import UIKit
import SlashConfig

class MyView: UIView {
  let subview = UIView()/.backgroundColor(.red)
  // ...
}

Motivation

Consider this as your given type:

struct Starship {
  var commandingOfficer: String
  var registry: String
  var isActive: Bool
}

extension Starship {
  static let titan = Starship(
    commandingOfficer: "William T. Riker",
    registry: "NCC-80102",
    isActive: false
  )
}

Creating a new version of Starship.titan requires you to use a var.

var titanRefit = Starship.titan
titanRefit.commandingOfficer = "Liam Shaw"
titanRefit.registry = "NCC-80102-A"
titanRefit.isActive = true

This way has some disadvantages. For example you are not protected for unintentionally further mutate titanRefit as it stays mutable for the rest of the scope. In other cases it is just a lot of ceremony to just change one property of one provided value.

But more importantly: This syntax does not work in all places. For example it is not possible to configure properties of members of a class at the location where you define them. In this case you need to make sure the member is mutable and the first place you can mutate them is inside init().

class TVShow {
  var starship = Starship.titan
  
  init() {
    starship.commandingOfficer = "Liam Shaw"
    starship.registry = "NCC-80102-A"
    starship.isActive = true
  } 
}

// or (if you want keep using `let`)

class TVShow {
  let starship: Starship
  
  init() {
    var starship = Starship.titan
    starship.commandingOfficer = "Liam Shaw"
    starship.registry = "NCC-80102-A"
    starship.isActive = true
    self.starship = starship 
  } 
}

With SlashConfig

With SlashConfig you can mutate all properties of a value wherever you can access or define it and you can even keep it non-mutating.

import SlashConfig

class TVShow {
  let starship = Starship.titan/
    .commandingOfficer("Liam Shaw")/
    .registry("NCC-80102-A")/
    .isActive(true)
  
  init() { }
}

// or

class TVShow {
  let starship = Starship.titan/ {
    $0.commandingOfficer = "Liam Shaw"
    $0.registry = "NCC-80102-A"
    $0.isActive = true
  }
  
  init() { }
}