Code Quality Rank: L5
Programming language: Swift
License: MIT License
Tags: JSON    
Latest version: v0.3.2

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Coverage Status Build Status MIT licensed CocoaPods Swift

Lazily deserialize JSON into strongly typed Swift objects, with a few getter style options.

Is your app using it? Let me know!


Quickly install using CocoaPods:

pod 'LazyObject'

Or manually install:

  1. Clone this repository
  2. Build the LazyObject project
  3. Add the resulting framework file to your project
  4. ?
  5. Profit


Let's look at an example model to show off some of the functionality:

class Bank: LazyObject {
    var money: Double       { return try! objectFor(#function) } // Automagically converts #function to a "money" string
    var getPaid: Bool?      { return try? objectFor("get_paid") } // Will be nil if called and key/value don't exist
    var security: [Person]? { return try? objectFor(#function) } // Works with arrays of other LazyObjects as well
    var debt: Double        { return try! objectFor("accounting.books.cooked") } // Nested key paths are supported 

Models are instantiated from JSON dictionaries:

// The dictionary passed here is the JSON response
let bank = Bank(dictionary: ["money": 9999, "get_paid": true])

There is also a convenience extension for instantiating from JSON arrays:

let banks = Bank.fromArray(jsonArrayOfDictionaries)

Date Formattables

Since many services have varying date formats, LazyObject provides an easy way to specify which standard or custom format you'd like to conform to.

class Retirement: LazyObject, ISO8601Formattable {
  var date: NSDate?   { return try? dateFor(#function) }

Note: For dates, you must specifically use the dateFor() method so it will choose the correct formatter from the cache.

Any of your base or sub-classes can conform to one of the supported protocols:

  • ISO8601Formattable (e.g. "2016-04-24T14:42:42.424Z")
  • RFC3339Formattable (e.g. "2016-04-24T14:42:42Z")
  • RFC1123Formattable (e.g. "Sun, 24 Apr 2016 14:42:42 +0000")
  • RFC850Formattable (e.g. "Sunday, 24-Apr-16 14:42:42 UTC")
  • EpochFormattable (e.g. "1461508962.424" as a string or 1461508962.424 as a double)

Or you're free to extend LazyDateFormattable to create custom date conversions (look at how the above protocols are implemented for an example).

All formatters above are created once and cached for re-use, and it is recommended you do the same if you create custom formattables since they tend to be expensive to create.

Key Getter Options

The objectFor method supports a couple variations for key names:

  • #function: Converts whatever the property name is into a string (e.g. var help becomes "help"). Note that a property name like myProperty will be converted to "myProperty" not my_property, so feel free to extend LazyObject if you require that.
  • keyPath: Can be a string containing a single key like first_name or a key path to a nested value like location.latitude


Notice in the example that you can use try? to ensure optional safety on the properties. If you're feeling confident, you can use try! to force it but you may receive one of a few runtime errors if it doesn't succeed.


Aside from standard JSON data types, the following types are seamlessly supported:

  • NSDate
  • NSNumber

Custom Convertibles

If you want to seamlessly convert a custom value, such as to create an NSNumber from a string value, you can create your own extensions of LazyConvertible like so:

// Note: this example is actually already part of the library, so no need to extend NSNumber

import Foundation

extension NSNumber: LazyConvertible {

    public static func convert(value: AnyObject?) throws -> NSNumber {
        guard let string = value as? String else {
            throw LazyMappingError.UnexpectedTypeError(value: value, type: String.self)

        let formatter = NSNumberFormatter()
        guard let number = formatter.numberFromString(string) else {
            throw LazyMappingError.CustomError(message: "'\(string)' is not a valid input for NSNumber instantiation")

        return number


This will allow you to seamlessly support any type of valid NSNumber, whether from string or from a number value, just by using the normal objectFor methods.

Setting Values

LazyObject is focused mostly on read-only models, but you can still easily expose a setter on the model if necessary:

class Object: LazyObject {
    var id: NSNumber? {
        get {
            return try? objectFor(#function)
        set {
            setObject(newValue, setter: #function)

Note: Similar to the getter methods, both the setter #function can be used or the keyPath can be used to reference the key name to update.


Swift, ARC & iOS 9+

A little help from my friends

Please feel free to fork and create a pull request for bug fixes or improvements, being sure to maintain the general coding style, adding tests, and adding comments as necessary.


This library is influenced by CottonObject and Mapper

*Note that all licence references and agreements mentioned in the LazyObject README section above are relevant to that project's source code only.