Builder is Swift builder pattern library that utilize dynamicCallable and dynamicMemberLookup as its core.

What's New


  • Rename Buildable to Initializable
  • Add another Buildable that can build an object using bld computed property


Builder is Swift builder pattern library that utilize dynamicCallable and dynamicMemberLookup as its core.

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To run the example project, clone the repo, and run pod install from the Example directory first.


  • Swift 5.1 or higher (or 5.3 when using Swift Package Manager)
  • iOS 10 or higher

Only Swift Package Manager

  • macOS 10.10 or higher
  • tvOS 10 or higher



Builder is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'Builder', '~> 1.1.0'

Swift Package Manager from XCode

  • Add it using XCode menu File > Swift Package > Add Package Dependency
  • Add as Swift Package URL
  • Set rules at version, with Up to Next Major option and put 1.1.0 as its version
  • Click next and wait

Swift Package Manager from Package.swift

Add as your target dependency in Package.swift

dependencies: [
  .package(url: "", .upToNextMajor(from: "1.1.0"))

Use it in your target as Builder

  name: "MyModule",
  dependencies: ["Builder"]


Nayanda Haberty,


Impose is available under the MIT license. See the LICENSE file for more info.

Basic Usage

Using Builder is simple. You just need to pass the object you want to build and assign its writable property as its a function. Example:

If you have a class like this:

class MyObject {
    var string: String?
    var int: Int?
    var double: Double?

you can build it like this:

let myObject: MyObject = builder(MyObject())
    .string("some string")

Its even can assign property of property as deep as you need, as long the property is mutable:

let myObject: MyObject = builder(MyObject())
    .string("some string")
    .subObject.string("some string")


There's a protocol named Buildable that allowed your object to have a bld computed property that will return a Builder object for you to use:

let myObject: MyObject = MyBuildable().bld
    .string("some string")
    .subObject.string("some string")


There's a protocol named Initializable which declared like this:

public protocol Initializable {

its just to ensure you can call builder global function by only passing its Type:

let view: MyObjectImplementInitializable = builder(MyObjectImplementInitializable.self)
    .string("some string")

Initializable is implementing Buildable by default

Error Handling

Sometimes you can mistakenly try to assigning property that immutable. By default you can always see the debugPrint output like this:

Failed to assign property keypath of MyType with property type MyPropertyType because its not writable

But it can be forgotton and became a bug in the future. So you can always force it to throw fatalError if something like this is happes by assigning errorHandling on BuilderConfig:

BuilderConfig.errorHandling = .fatalErrorOnAssigningLet

it will create a fatal error when immutable property is assigned, so you can always fix it before it became a problem in the future. You can always handling it manually by assigning closure:

BuilderConfig.errorHandling = .manual { message in
    debugPrint("FIX THIS: \(message)")


You know how, just clone and do pull request


  • Swift Tools 5.3.0
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Last updated: Tue Jan 10 2023 15:26:27 GMT-0500 (GMT-05:00)