Conform to Codable Add CodingKeys for snake_case Use var instead of let Conform to Identifiable

Struct name:

Features

🍎 Codable Protocol

Encodable & Decodable
Nested struct generation
Proper Swift type mapping
Foundation import included

🔑 CodingKeys Support

Auto snake_case to camelCase
CodingKeys enum generated
Maps JSON keys correctly
Optional key customization

⚡ Smart Type Detection

Int vs Double inference
Bool, String, optional types
Array type [T] generation
Identifiable conformance option

Swift Codable Guide

Swift Codable Protocol

Codable is Swift's type-safe serialization protocol. It combines Encodable and Decodable, enabling you to convert between Swift types and JSON with minimal code.

import Foundation

struct User: Codable {
    let id: Int
    let name: String
    let isActive: Bool

    enum CodingKeys: String, CodingKey {
        case id
        case name
        case isActive = "is_active"
    }
}

Decoding JSON with JSONDecoder

import Foundation

let jsonData = """
{"id": 1, "name": "Alice", "is_active": true}
""".data(using: .utf8)!

let decoder = JSONDecoder()
let user = try! decoder.decode(User.self, from: jsonData)
print(user.name) // Alice

// Encoding back to JSON
let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
let encoded = try! encoder.encode(user)
print(String(data: encoded, encoding: .utf8)!)

Common Use Cases

iOS Apps: Model REST API responses in Swift apps with URLSession
macOS Apps: Parse configuration files or API data
SwiftUI: Data models for @State and @ObservableObject
Combine: Decode publishers from network requests
Core Data: Map JSON to Core Data entities

FAQ

Q: When do I need CodingKeys?

A: You need CodingKeys when the JSON key names differ from your Swift property names — most commonly when the JSON uses snake_case and your Swift uses camelCase.

Q: let vs var — which is better?

A: Prefer let for immutable model types. Swift encourages value semantics and immutability. Use var only if you need to mutate properties after decoding.

Decoding JSON reliably with Codable

Codable turns JSON into Swift types with very little code. The catch is that a single mismatched field makes the whole decode fail, so it helps to plan for the variations real APIs produce.

Tips and common pitfalls

Set decoder.keyDecodingStrategy = .convertFromSnakeCase to map user_name to userName without writing CodingKeys.
Use optionals for any field the server may omit or send as null.
Set decoder.dateDecodingStrategy = .iso8601 when timestamps are ISO 8601 strings.
When decoding fails, print the DecodingError; its context names the exact key path that did not match.

JSON to Swift Codable