Builder

Constructs complex objects step by step using a fluent interface, separating construction from representation.

The Problem

A class with many optional parameters leads to telescoping constructors or long init calls that are hard to read. You need a clean way to build objects incrementally.

How It Works

›Method chaining (fluent interface) makes construction readable
›Same builder can produce different representations
›Validates required fields only at build() time
›Immutable result: once built, the object is complete
›Avoids the "telescoping constructor" anti-pattern

When to Use

✓Objects with many optional or configurable fields

✓When the object requires multi-step construction

✓When you want to create different configurations of the same object type

✓HTTP request builders, query builders, notification payloads

Real-World Examples

🍎

iOS

URLComponents, NSAttributedString, UIAlertController + addAction calls

🤖

Android

AlertDialog.Builder, Notification.Builder, OkHttpClient.Builder

🌐

Web

URLSearchParams, axios config, Knex/TypeORM query builders

Code Examples

Swift

struct PushPayload {
    let title: String
    let body: String
    let badge: Int
    let sound: String
    let category: String?
}

final class PushPayloadBuilder {
    private var title = ""
    private var body  = ""
    private var badge = 0
    private var sound = "default"
    private var category: String?

    func title(_ v: String)    -> Self { title    = v; return self }
    func body(_ v: String)     -> Self { body     = v; return self }
    func badge(_ v: Int)       -> Self { badge    = v; return self }
    func sound(_ v: String)    -> Self { sound    = v; return self }
    func category(_ v: String) -> Self { category = v; return self }

    func build() -> PushPayload {
        PushPayload(title: title, body: body, badge: badge,
                    sound: sound, category: category)
    }
}

let payload = PushPayloadBuilder()
    .title("New Message")
    .body("You have 3 unread messages")
    .badge(3)
    .category("MESSAGE")
    .build()