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https://github.com/Anviking/Decodable

[Probably deprecated] Swift 2/3 JSON unmarshalling done (more) right
https://github.com/Anviking/Decodable

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[Probably deprecated] Swift 2/3 JSON unmarshalling done (more) right

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# Decodable

Simple and strict, yet powerful object mapping made possible by Swift 2's error handling. Greatly inspired by [Argo](http://github.com/thoughtbot/Argo), but without a bizillion functional operators.



[![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)

[![Cocoapods version](https://cocoapod-badges.herokuapp.com/v/Decodable/badge.png)](https://cocoapods.org/pods/Decodable)

[![Platforms](https://cocoapod-badges.herokuapp.com/p/Decodable/badge.png)](https://cocoadocs.org/docsets/NSStringMask)

[![Travis](https://img.shields.io/travis/Anviking/Decodable/master.svg)](https://travis-ci.org/Anviking/Decodable/branches)



```swift



struct Repository {

    let name: String

    let description: String

    let stargazersCount: Int

    let language: String?

    let sometimesMissingKey: String?

    

    let owner: User // Struct conforming to Decodable

    let defaultBranch: Branch // Struct NOT conforming to Decodable

    

    var fullName: String { return "\(owner.login)/\(name)" }

}



extension Repository: Decodable {

    static func decode(j: Any) throws -> Repository {

        return try Repository(

                    name: j => "nested" => "name", 

                    description: j => "description", 

                    stargazersCount: j => "stargazers_count", 

                    language: j => "language", 

                    sometimesMissingKey: j =>? "sometimesMissingKey",

                    owner: j => "owner", 

                    defaultBranch: Branch(name: j => "default_branch")

                )

    }

}



do {

    let json = try NSJSONSerialization.JSONObjectWithData(data, options: [])

    let repo = try [Repository].decode(json)

} catch {

    print(error)

}

```



## How does it work?



### A protocol

```swift

public protocol Decodable {

    static func decode(json: Any) throws -> Self

}

```

### A parse-function

```swift

public func parse(json: Any, path: [String], decode: (Any throws -> T)) throws -> T

```



### And shameless operator-overloading

The too-many generated overloads, all calling the `parse`-function, can be found in [Overloads.swift](https://github.com/Anviking/Decodable/blob/master/Sources/Overloads.swift). Return types include `T?`, `[T?]`, `[T?]?`, `Any` and `[String: T]?`. When conditional protocol conformance is supported in Swift this won't be necessary, and automagic decoding of infinitly nested generic types (like `[[[[[[[[[A???]]: B]]]?]]?]]`) would work.



An overload may look like this:

```swift

public func => (json: Any, keyPath: KeyPath) throws -> T

```



## KeyPaths

Keypaths can be created from string and array literals as well as with explicit initializers. They can also be joined using the operators `=>` and `=>?`. `=>?` is another operator that indicates that `nil` should be returned if the key to the right is missing.



- When composing `=>` and `=>?` operators in the same keypath, the strictness of `=>` is still honoured.

- Optional key paths (`=>?`) require an optional return type



```swift

let a: KeyPath = "a"

let b: KeyPath = ["a", "b"]

let c: KeyPath = "a" => "b" => "c"

let string: String? = json =>? "key1" => "key2" => "key3"`

                                ^^^^ allowed to be missing

```

## Errors

Errors will be caught and rethrown in the decoding process to backpropagate metadata, like the JSON object that failed decoding, the key path to it, and the root JSON object.



From [DecodingError.swift](https://github.com/anviking/decodable/tree/master/Sources/DecodingError.swift):

```swift

public enum DecodingError: ErrorProtocol, Equatable {

    /// Thrown when optional casting from `Any` fails.

    ///

    /// This can happen both when trying to access a key on a object

    /// that isn't a `NSDictionary`, and failing to cast a `Castable`

    /// primitive.

    case typeMismatch(expected: Any.Type, actual: Any.Type, Metadata)

    

    /// Thrown when a given, required, key was not found in a dictionary.

    case missingKey(String, Metadata)

    

    /// Thrown from the `RawRepresentable` extension when

    /// `init(rawValue:)` returned `nil`.

    case rawRepresentableInitializationError(rawValue: Any, Metadata)

    

    /// When an error is thrown that isn't `DecodingError`, it 

    /// will be wrapped in `DecodingError.other` in order to also provide

    /// metadata about where the error was thrown.

    case other(ErrorProtocol, Metadata)

}

```



```swift

let dict: NSDictionary = ["object": ["repo": ["owner": ["id" : 1, "login": "anviking"]]]]



do {

    let username: String = try dict => "object" => "repo" => "owner" => "name"

} catch let error {

    print(error)

}

//

// MissingKeyError at object.repo.owner: name in {

//    id = 1;

//    login = anviking;

// }

```



## Handling Errors

Expressions like `j => "key"` will throw directly, and `catch`-statements can be used to create the most complex error handling behaviours. This also means that `try?` can be used to return nil if *anything* goes wrong instead of throwing.



For convenience there is an operator, `=>?`, that only returns nil on missing keys, for APIs that indicate `null` in that manner, and to aid working with different response formats.



| Overload | Null Behaviour | Missing Key Behavior  |Type Mismatch Behaviour | Errors in subobjects | 

| ------------- |:-------------:|:-----:|:-----:|:-----:|

|  `=> -> T`| throws | throws | throws | uncaught (throws) | 

|  `=> -> T?`| nil | throws | throws | uncaught (throws) | 

|  `=>? -> T?`| nil | nil | throws | uncaught (throws) | 

|  `try? => -> T `| nil | nil | nil | caught (nil) | 



## Customization

`Int`, `Double`,`String`, `Bool`, `Date` (ISO8601), `NSArray`, and `NSDictionary` types that conform to `DynamicDecodable` with the following declaration:

```swift

public protocol DynamicDecodable {

    associatedtype DecodedType

    static var decoder: (Any) throws -> DecodedType {get set}

}

```

This allows Decodable to implement default decoding closures while allowing you to override them as needed.

```swift

// Lets extend Bool.decoder so that it accepts certain strings:

Bool.decoder = { json in

    switch json {

    case let str as String where str == "true":

        return true

    case let str as String where str == "false":

        return false

    default:

        return try cast(json)

    }

}

```



Note that when extending new types to conform to `Decodable` there is really no point in conforming to `DynamicDecodable` since you already control the implementation. Also note that the `decoder` properties are intended as "set once". If you need different behaviour on different occations, please create custom decode functions.



The default `Date.decoder` uses a ISO8601 date formatter. If you don't want to create your own decode closure there's a helper:

```swift

Date.decoder = Date.decoder(using: formatter)

```



## When `Decodable` isn't enough

Don't be afraid of not conforming to `Decodable`.

```swift

let array = try NSArray.decode(json => "list").map {

    try Contribution(json: $0, repository: repo)

}

```



## Tips

- You can use `Decodable` with classes. Just make sure to either call a `required` initializer on self (e.g `self.init`) and return `Self`, or make your class `final`. ( [This](http://stackoverflow.com/questions/26495586/best-practice-to-implement-a-failable-initializer-in-swift) might be a problem though)

- The `Decodable`-protocol and the `=>`-operator should in no way make you committed to use them everywhere.



## Compatibility



| Swift version | Compatible tag or branch |

| --- | --- |

| Swift 4.0 | `0.6.0` |

| Swift 3.0 | `v0.5` |

| Swift 2.3 | `v0.4.4`|

| Swift 2.2 | `v0.4.3`|



## Note on Swift 4.0 usage

Due to collisions with the standard library you will have to import ambiguous symbols specifically, in addition to `Decodable` as a whole.



This means you likely want the following

```swift

import Decodable

import protocol Decodable.Decodable

```

and you can import other symbols, e.g `KeyPath`, `DecodingError`, in a simlilar fashion (using `import struct` and `import enum`)