Himotoki

Himotoki (紐解き) is a type-safe JSON decoding library written purely in Swift. This library is highly inspired by the popular Swift JSON parsing libraries: Argo and ObjectMapper.

Himotoki has the same meaning of ‘decoding’ in Japanese.

• Just do JSON decoding (deserialization) well. JSON encoding (serialization) will not be supported going forward.
• Much simpler API.
• Fail-fast conditional model building. This is useful for some structs with non-optional let properties.
• No external dependencies.

Let’s take a look at a simple example:

struct Group: Himotoki.Decodable {
    let name: String
    let floor: Int
    let locationName: String
    let optional: [String]?

    // MARK: Himotoki.Decodable

    static func decode(_ e: Extractor) throws -> Group {
        return try Group(
            name: e <| "name",
            floor: e <| "floor",
            locationName: e <| [ "location", "name" ], // Parse nested objects
            optional: e <|? "optional" // Parse optional arrays of values
        )
    }
}

func testGroup() {
    var JSON: [String: AnyObject] = [ "name": "Himotoki", "floor": 12 ]
    
    let g = try? Group.decodeValue(JSON)
    XCTAssert(g != nil)
    XCTAssert(g?.name == "Himotoki")
    XCTAssert(g?.floor == 12)
    XCTAssert(g?.optional == nil)

    JSON["name"] = nil
    do {
        try Group.decodeValue(JSON)
    } catch let DecodeError.MissingKeyPath(keyPath) {
        XCTAssert(keyPath == "name")
    } catch {
        XCTFail()
    }
}

Please note that you should need to add the module name Himotoki to Decodable (Himotoki.Decodable) to avoid type name collision with Foundation.Decodable in Xcode 9 or later.

Implementing the decode method for your models

To implement the decode method for you models conforming to the Decodable protocol, you can use the following Extractor‘s extraction methods:

• public func value<T: Decodable>(_ keyPath: KeyPath) throws -> T
• public func valueOptional<T: Decodable>(_ keyPath: KeyPath) throws -> T?
• public func array<T: Decodable>(_ keyPath: KeyPath) throws -> [T]
• public func arrayOptional<T: Decodable>(_ keyPath: KeyPath) throws -> [T]?
• public func dictionary<T: Decodable>(_ keyPath: KeyPath) throws -> [String: T]
• public func dictionaryOptional<T: Decodable>(_ keyPath: KeyPath) throws -> [String: T]?

Extraction Operators

Himotoki also supports the following operators to decode JSON elements, where T is a generic type conforming to the Decodable protocol.

Operator	Decode element as	Remarks
<|	T	A value
<|?	T?	An optional value
<||	[T]	An array of values
<||?	[T]?	An optional array of values
<|-|	[String: T]	A dictionary of values
<|-|?	[String: T]?	An optional dictionary of values

Value Transformation

You can transform an extracted value to an instance of non-Decodable types by passing the value to a Transformer instance as follows:

// Creates a `Transformer` instance.
let URLTransformer = Transformer<String, URL> { urlString throws -> URL in
    if let url = URL(string: urlString) {
        return url
    }
    
    throw customError("Invalid URL string: \(urlString)")
}

let url: URL = try URLTransformer.apply(e <| "foo_url")
let otherURLs: [URL] = try URLTransformer.apply(e <| "bar_urls")

Requirements

Himotoki 4.x requires / supports the following environments:

• Swift 4.2 / Xcode 10.1 or later
• OS X 10.9 or later
• iOS 8.0 or later
• tvOS 9.0 or later
• watchOS 2.0 or later
• Linux is also supported

Installation

Currently Himotoki supports installation via the package managers Carthage and CocoaPods.

Carthage

Himotoki is Carthage compatible.

• Add github "ikesyo/Himotoki" ~> 3.1 to your Cartfile.
• Run carthage update.

CocoaPods

Himotoki also can be used by CocoaPods.

• Add the followings to your Podfile:

  use_frameworks!
  pod "Himotoki", "~> 3.1"

• Run pod install.

License

Himotoki is released under the MIT License.