Swiftpack.co - Package - jpsim/Yams



A sweet and swifty Yaml parser built on libYAML.



Building Yams on macOS requires Xcode 9.x or a Swift 3.2/4.x toolchain with the Swift Package Manager.

Building Yams on Linux requires a Swift 4.x compiler and Swift Package Manager to be installed.

Swift Package Manager

Add .package(url: "https://github.com/jpsim/Yams.git", from: "0.5.0") to your Package.swift file's dependencies.


Add pod 'Yams' to your Podfile.


Add github "jpsim/Yams" to your Cartfile.


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.
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 == """

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


  • 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


Both Yams and libYAML are MIT licensed.