Docs.md

Yams Documentation

For installation instructions, see README.md.

API documentation available at jpsim.com/Yams.

Usage

Consume YAML

Here's a simple example parsing a YAML array of strings:

import Yams

let yamlString = """
  - a
  - b
  - c
  """
do {
  let yamlNode = try Yams.load(yaml: yamlString)
  if let yamlArray = yamlNode as? [String] {
    print(yamlArray)
  }
} catch {
  print("handle error: \(error)")
}

// Prints:
// ["a", "b", "c"]

Emit YAML

Here's a simple example emitting YAML string from a Swift Array<String>:

import Yams

do {
  let yamlString = try Yams.serialize(node: ["a", "b", "c"])
  print(yamlString)
} catch {
  print("handle error: \(error)")
}

// Prints:
// - a
// - b
// - c

You can even customize the style:

import Yams

var node: Node = ["a", "b", "c"]
node.sequence?.style = .flow

do {
  let yamlString = try Yams.serialize(node: node)
  print(yamlString)
} catch {
  print("handle error: \(error)")
}

// Prints:
// [a, b, c]

Customize Parsing

For example, say you only want the literals true and false to represent booleans, unlike the YAML spec compliant boolean which also includes on/off and many others.

You can customize Yams' Constructor map:

import Yams

extension Constructor {
  public static func withBoolAsTrueFalse() -> Constructor {
    var map = defaultMap
    map[.bool] = Bool.constructUsingOnlyTrueAndFalse
    return Constructor(map)
  }
}

private extension Bool {
  static func constructUsingOnlyTrueAndFalse(from node: Node) -> Bool? {
    assert(node.isScalar)
    switch node.scalar!.string.lowercased() {
    case "true":
      return true
    case "false":
      return false
    default:
      return nil
    }
  }
}

private extension Node {
  var isScalar: Bool {
    if case .scalar = self {
      return true
    }
    return false
  }
}

// Usage:

let yamlString = """
  - true
  - on
  - off
  - false
  """
if let array = try? Yams.load(yaml: yamlString, .default, .withBoolAsTrueFalse()) as? [Any] {
  print(array)
}

// Prints:
// [true, "on", "off", false]

Expanding Environment Variables

For example:

import Yams

extension Constructor {
  public static func withEnv(_ env: [String: String]) -> Constructor {
    var map = defaultMap
    map[.str] = String.constructExpandingEnvVars(env: env)
    return Constructor(map)
  }
}

private extension String {
  static func constructExpandingEnvVars(env: [String: String]) -> (_ node: Node) -> String? {
    return { (node: Node) -> String? in
      assert(node.isScalar)
      return node.scalar!.string.expandingEnvVars(env: env)
    }
  }

  func expandingEnvVars(env: [String: String]) -> String {
    var result = self
    for (key, value) in env {
      result = result.replacingOccurrences(of: "${\(key)}", with: value)
    }

    return result
  }
}

// Usage:

let yamlString = """
  - first
  - ${SECOND}
  - SECOND
  """
let env = ["SECOND": "2"]
if let array = try? Yams.load(yaml: yamlString, .default, .withEnv(env)) as? [String] {
  print(array)
}

// Prints:
// ["first", "2", "SECOND"]

Converting Between Formats

Because Yams conforms to Swift 4's Codable protocol and provides a YAML Encoder and Decoder, you can easily convert between YAML and other formats that also provide Swift 4 Encoders and Decoders, such as JSON and Plist.

Error Handling

Failable operations in Yams throw Swift errors.

Types

Name	Yams Tag	YAML Tag	Swift Types
...	implicit	``	...
...	nonSpecific	!	...
String	str	tag:yaml.org,2002:str	String
Sequence	seq	tag:yaml.org,2002:seq	Array<Any>
Map	map	tag:yaml.org,2002:map	Dictionary<AnyHashable, Any>
Boolean	bool	tag:yaml.org,2002:bool	Bool
Floating Point	float	tag:yaml.org,2002:float	...
Null	null	tag:yaml.org,2002:null	Void
Integer	int	tag:yaml.org,2002:int	FixedWidthInteger
...	binary	tag:yaml.org,2002:binary	Data
...	merge	tag:yaml.org,2002:merge	...
...	omap	tag:yaml.org,2002:omap	...
...	pairs	tag:yaml.org,2002:pairs	...
Set	set	tag:yaml.org,2002:set	Set<AnyHashable>
Timestamp	timestamp	tag:yaml.org,2002:timestamp	Date
...	value	tag:yaml.org,2002:value	...
YAML	yaml	tag:yaml.org,2002:yaml	Unsupported