Yams

A sweet and swifty YAML parser built on LibYAML.

Installation

Building Yams requires Xcode 14.0+ or a Swift 5.7+ toolchain with the Swift Package Manager or CMake and Ninja.

CMake

CMake 3.17.2 or newer is required, along with Ninja 1.9.0 or newer.

When building for non-Apple platforms:

cmake -B /path/to/build -G Ninja -S /path/to/yams -DCMAKE_BUILD_TYPE=Release -DFoundation_DIR=/path/to/foundation/build/cmake/modules
cmake --build /path/to/build

To build for Apple platforms (macOS, iOS, tvOS, watchOS), there is no need to separately build Foundation because it is included as part of the SDK:

cmake -B /path/to/build -G Ninja -S /path/to/yams -DCMAKE_BUILD_TYPE=Release
cmake --build /path/to/build

Swift Package Manager

Add .package(url: "https://github.com/jpsim/Yams.git", from: "6.2.2") to your Package.swift file's dependencies.

Bazel

In your WORKSPACE file

YAMS_GIT_SHA = "SOME_SHA"
http_archive(
    name = "com_github_jpsim_yams",
    urls = [
        "https://github.com/jpsim/Yams/archive/%s.zip" % YAMS_GIT_SHA,
    ],
    strip_prefix = "Yams-%s" % YAMS_GIT_SHA,
)

Usage

Yams has three groups of conversion APIs: one for use with Codable types, another for Swift Standard Library types, and a third one for a Yams-native representation.

Codable types

• Codable is an encoding & decoding strategy introduced in Swift 4 enabling easy conversion between YAML and other Encoders like JSONEncoder and PropertyListEncoder.
• Lowest computational overhead, equivalent to Yams.Node.
• Encoding: YAMLEncoder.encode(_:) Produces a YAML String from an instance of type conforming to Encodable.
• Decoding: YAMLDecoder.decode(_:from:) Decodes an instance of type conforming to Decodable from YAML String or Data.

import Foundation
import Yams

struct S: Codable {
    var p: String
}

let s = S(p: "test")
let encoder = YAMLEncoder()
let encodedYAML = try encoder.encode(s)
encodedYAML == """
p: test

"""
let decoder = YAMLDecoder()
let decoded = try decoder.decode(S.self, from: encodedYAML)
s.p == decoded.p

Swift Standard Library types

• The type of Swift Standard Library is inferred from the contents of the internal Yams.Node representation by matching regular expressions.
• This method has the largest computational overhead When decoding YAML, because the type inference of all objects is done up-front.
• It may be easier to use in such a way as to handle objects created from JSONSerialization or if the input is already standard library types (Any, Dictionary, Array, etc.).
• Encoding: Yams.dump(object:) Produces a YAML String from an instance of Swift Standard Library types.
• Decoding: Yams.load(yaml:) Produces an instance of Swift Standard Library types as Any from YAML String.

// [String: Any]
let dictionary: [String: Any] = ["key": "value"]
let mapYAML: String = try Yams.dump(object: dictionary)
mapYAML == """
key: value

"""
let loadedDictionary = try Yams.load(yaml: mapYAML) as? [String: Any]

// [Any]
let array: [Int] = [1, 2, 3]
let sequenceYAML: String = try Yams.dump(object: array)
sequenceYAML == """
- 1
- 2
- 3

"""
let loadedArray: [Int]? = try Yams.load(yaml: sequenceYAML) as? [Int]

// Any
let string = "string"
let scalarYAML: String = try Yams.dump(object: string)
scalarYAML == """
string

"""
let loadedString: String? = try Yams.load(yaml: scalarYAML) as? String

Yams.Node

• Yams' native model representing Nodes of YAML which provides all functions such as detection and customization of the YAML format.
• Depending on how it is used, computational overhead can be minimized.
• Encoding: Yams.serialize(node:) Produces a YAML String from an instance of Node.
• Decoding Yams.compose(yaml:) Produces an instance of Node from YAML String.

var map: Yams.Node = [
    "array": [
        1, 2, 3
    ]
]
map.mapping?.style = .flow
map["array"]?.sequence?.style = .flow
let yaml = try Yams.serialize(node: map)
yaml == """
{array: [1, 2, 3]}

"""
let node = try Yams.compose(yaml: yaml)
map == node

NSMutable* compatibility

Yams also supports deep conversion of YAML into NSMutableDictionary and NSMutableArray, which is useful when working with mutable Cocoa-style collections, such as NSMutableDictionary and NSMutableArray.

To produce NSMutable* results, use a custom constructor:

let yaml = """
names:
  - Alice
  - Bob
"""

let constructor = Constructor(Constructor.defaultScalarMap,
                              Constructor.nsMutableMappingMap,
                              Constructor.nsMutableSequenceMap)

let result = try Yams.load(yaml: yaml, .default, constructor) as? NSMutableDictionary
let names = result?["names"] as? NSMutableArray
print(names ?? "No data") // -> (Alice, Bob)

Integrating with Combine

When Apple's Combine framework is available, YAMLDecoder conforms to the TopLevelDecoder protocol, which allows it to be used with the decode(type:decoder:) operator:

import Combine
import Foundation
import Yams

func fetchBook(from url: URL) -> AnyPublisher<Book, Error> {
    URLSession.shared.dataTaskPublisher(for: url)
        .map(\.data)
        .decode(type: Book.self, decoder: YAMLDecoder())
        .eraseToAnyPublisher()
}

License

Both Yams and libYAML are MIT licensed.