Round-trip GeoJSON foreign members

Sources/Turf/Codable.swift

@@ -1,17 +1,19 @@
 import Foundation
-#if !os(Linux)
-import CoreLocation
-#endif
 
-extension Ring: Codable {
-    public init(from decoder: Decoder) throws {
-        let container = try decoder.singleValueContainer()
-        self = Ring(coordinates: try container.decode([LocationCoordinate2DCodable].self).decodedCoordinates)
+/**
+ A coding key as an extensible enumeration.
+ */
+struct AnyCodingKey: CodingKey {
+    var stringValue: String
+    var intValue: Int?
+
+    init?(stringValue: String) {
+        self.stringValue = stringValue
+        self.intValue = nil
     }
 
-    public func encode(to encoder: Encoder) throws {
-        var container = encoder.singleValueContainer()
-        try container.encode(coordinates.codableCoordinates)
+    init?(intValue: Int) {
+        self.stringValue = String(intValue)
+        self.intValue = intValue
     }
 }
-

Sources/Turf/Feature.swift

@@ -6,7 +6,7 @@ import CoreLocation
 /**
  A [Feature object](https://datatracker.ietf.org/doc/html/rfc7946#section-3.2) represents a spatially bounded thing.
  */
-public struct Feature: Equatable {
+public struct Feature: Equatable, ForeignMemberContainer {
     /**
      A string or number that commonly identifies the feature in the context of a data set.
 
@@ -20,6 +20,8 @@ public struct Feature: Equatable {
     /// The geometry at which the feature is located.
     public var geometry: Geometry?
 
+    public var foreignMembers: JSONObject = [:]
+
     /**
      Initializes a feature located at the given geometry.
 
@@ -57,6 +59,7 @@ extension Feature: Codable {
         geometry = try container.decodeIfPresent(Geometry.self, forKey: .geometry)
         properties = try container.decodeIfPresent(JSONObject.self, forKey: .properties)
         identifier = try container.decodeIfPresent(FeatureIdentifier.self, forKey: .identifier)
+        try decodeForeignMembers(notKeyedBy: CodingKeys.self, with: decoder)
     }
 
     public func encode(to encoder: Encoder) throws {
@@ -65,5 +68,6 @@ extension Feature: Codable {
         try container.encode(geometry, forKey: .geometry)
         try container.encodeIfPresent(properties, forKey: .properties)
         try container.encodeIfPresent(identifier, forKey: .identifier)
+        try encodeForeignMembers(notKeyedBy: CodingKeys.self, to: encoder)
     }
 }

Sources/Turf/FeatureCollection.swift

@@ -3,10 +3,12 @@ import Foundation
 /**
  A [FeatureCollection object](https://datatracker.ietf.org/doc/html/rfc7946#section-3.3) is a collection of Feature objects.
  */
-public struct FeatureCollection: Equatable {
+public struct FeatureCollection: Equatable, ForeignMemberContainer {
     /// The features that the collection contains.
     public var features: [Feature] = []
 
+    public var foreignMembers: JSONObject = [:]
+
     /**
      Initializes a feature collection containing the given features.
 
@@ -31,11 +33,13 @@ extension FeatureCollection: Codable {
         let container = try decoder.container(keyedBy: CodingKeys.self)
         _ = try container.decode(Kind.self, forKey: .kind)
         features = try container.decode([Feature].self, forKey: .features)
+        try decodeForeignMembers(notKeyedBy: CodingKeys.self, with: decoder)
     }
 
     public func encode(to encoder: Encoder) throws {
         var container = encoder.container(keyedBy: CodingKeys.self)
         try container.encode(Kind.FeatureCollection, forKey: .kind)
         try container.encode(features, forKey: .features)
+        try encodeForeignMembers(notKeyedBy: CodingKeys.self, to: encoder)
     }
 }

Sources/Turf/GeoJSON.swift

@@ -89,3 +89,38 @@ extension Feature: GeoJSONObjectConvertible {
 extension FeatureCollection: GeoJSONObjectConvertible {
     public var geoJSONObject: GeoJSONObject { return .featureCollection(self) }
 }
+
+/**
+ A GeoJSON object that can contain [foreign members](https://datatracker.ietf.org/doc/html/rfc7946#section-6.1) in arbitrary keys.
+ */
+public protocol ForeignMemberContainer {
+    /// [Foreign members](https://datatracker.ietf.org/doc/html/rfc7946#section-6.1) to round-trip to JSON.
+    var foreignMembers: JSONObject { get set }
+}
+
+extension ForeignMemberContainer {
+    /**
+     Decodes any foreign members using the given decoder.
+     */
+    mutating func decodeForeignMembers<WellKnownCodingKeys>(notKeyedBy _: WellKnownCodingKeys.Type, with decoder: Decoder) throws where WellKnownCodingKeys: CodingKey {
+        let foreignMemberContainer = try decoder.container(keyedBy: AnyCodingKey.self)
+        for key in foreignMemberContainer.allKeys {
+            if WellKnownCodingKeys(stringValue: key.stringValue) == nil {
+                foreignMembers[key.stringValue] = try foreignMemberContainer.decode(JSONValue?.self, forKey: key)
+            }
+        }
+    }
+
+    /**
+     Encodes any foreign members using the given encoder.
+     */
+    func encodeForeignMembers<WellKnownCodingKeys>(notKeyedBy _: WellKnownCodingKeys.Type, to encoder: Encoder) throws where WellKnownCodingKeys: CodingKey {
+        var foreignMemberContainer = encoder.container(keyedBy: AnyCodingKey.self)
+        for (key, value) in foreignMembers {
+            if let key = AnyCodingKey(stringValue: key),
+               WellKnownCodingKeys(stringValue: key.stringValue) == nil {
+                try foreignMemberContainer.encode(value, forKey: key)
+            }
+        }
+    }
+}

Sources/Turf/Geometries/GeometryCollection.swift

@@ -6,10 +6,12 @@ import CoreLocation
 /**
  A [GeometryCollection geometry](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.8) is a heterogeneous collection of `Geometry` objects that are related.
  */
-public struct GeometryCollection: Equatable {
+public struct GeometryCollection: Equatable, ForeignMemberContainer {
     /// The geometries contained by the geometry collection.
     public var geometries: [Geometry]
 
+    public var foreignMembers: JSONObject = [:]
+
     /**
      Initializes a geometry collection defined by the given geometries.
 
@@ -50,11 +52,13 @@ extension GeometryCollection: Codable {
         _ = try container.decode(Kind.self, forKey: .kind)
         let geometries = try container.decode([Geometry].self, forKey: .geometries)
         self = .init(geometries: geometries)
+        try decodeForeignMembers(notKeyedBy: CodingKeys.self, with: decoder)
     }
 
     public func encode(to encoder: Encoder) throws {
         var container = encoder.container(keyedBy: CodingKeys.self)
         try container.encode(Kind.GeometryCollection, forKey: .kind)
         try container.encode(geometries, forKey: .geometries)
+        try encodeForeignMembers(notKeyedBy: CodingKeys.self, to: encoder)
     }
 }

Sources/Turf/Geometries/LineString.swift

@@ -6,10 +6,12 @@ import CoreLocation
 /**
  A [LineString geometry](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.4) is a collection of two or more positions, each position connected to the next position linearly.
  */
-public struct LineString: Equatable {
+public struct LineString: Equatable, ForeignMemberContainer {
     /// The positions at which the line string is located.
     public var coordinates: [LocationCoordinate2D]
 
+    public var foreignMembers: JSONObject = [:]
+
     /**
      Initializes a line string defined by given positions.
 
@@ -55,12 +57,14 @@ extension LineString: Codable {
         _ = try container.decode(Kind.self, forKey: .kind)
         let coordinates = try container.decode([LocationCoordinate2DCodable].self, forKey: .coordinates).decodedCoordinates
         self = .init(coordinates)
+        try decodeForeignMembers(notKeyedBy: CodingKeys.self, with: decoder)
     }
 
     public func encode(to encoder: Encoder) throws {
         var container = encoder.container(keyedBy: CodingKeys.self)
         try container.encode(Kind.LineString, forKey: .kind)
         try container.encode(coordinates.codableCoordinates, forKey: .coordinates)
+        try encodeForeignMembers(notKeyedBy: CodingKeys.self, to: encoder)
     }
 }
 

Sources/Turf/Geometries/MultiLineString.swift

@@ -6,10 +6,12 @@ import CoreLocation
 /**
  A [MultiLineString geometry](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.5) is a collection of `LineString` geometries that are disconnected but related.
  */
-public struct MultiLineString: Equatable {
+public struct MultiLineString: Equatable, ForeignMemberContainer {
     /// The positions at which the multi–line string is located. Each nested array corresponds to one line string.
     public var coordinates: [[LocationCoordinate2D]]
 
+    public var foreignMembers: JSONObject = [:]
+
     /**
      Initializes a multi–line string defined by the given positions.
 
@@ -46,11 +48,13 @@ extension MultiLineString: Codable {
         _ = try container.decode(Kind.self, forKey: .kind)
         let coordinates = try container.decode([[LocationCoordinate2DCodable]].self, forKey: .coordinates).decodedCoordinates
         self = .init(coordinates)
+        try decodeForeignMembers(notKeyedBy: CodingKeys.self, with: decoder)
     }
 
     public func encode(to encoder: Encoder) throws {
         var container = encoder.container(keyedBy: CodingKeys.self)
         try container.encode(Kind.MultiLineString, forKey: .kind)
         try container.encode(coordinates.codableCoordinates, forKey: .coordinates)
+        try encodeForeignMembers(notKeyedBy: CodingKeys.self, to: encoder)
     }
 }

Sources/Turf/Geometries/MultiPoint.swift

@@ -6,10 +6,12 @@ import CoreLocation
 /**
  A [MultiPoint geometry](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.3) represents a collection of disconnected but related positions.
  */
-public struct MultiPoint: Equatable {
+public struct MultiPoint: Equatable, ForeignMemberContainer {
     /// The positions at which the multipoint is located.
     public var coordinates: [LocationCoordinate2D]
 
+    public var foreignMembers: JSONObject = [:]
+
     /**
      Initializes a multipoint defined by the given positions.
 
@@ -35,11 +37,13 @@ extension MultiPoint: Codable {
         _ = try container.decode(Kind.self, forKey: .kind)
         let coordinates = try container.decode([LocationCoordinate2DCodable].self, forKey: .coordinates).decodedCoordinates
         self = .init(coordinates)
+        try decodeForeignMembers(notKeyedBy: CodingKeys.self, with: decoder)
     }
 
     public func encode(to encoder: Encoder) throws {
         var container = encoder.container(keyedBy: CodingKeys.self)
         try container.encode(Kind.MultiPoint, forKey: .kind)
         try container.encode(coordinates.codableCoordinates, forKey: .coordinates)
+        try encodeForeignMembers(notKeyedBy: CodingKeys.self, to: encoder)
     }
 }

Sources/Turf/Geometries/MultiPolygon.swift

@@ -6,10 +6,12 @@ import CoreLocation
 /**
  A [MultiPolygon geometry](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.7) is a collection of `Polygon` geometries that are disconnected but related.
  */
-public struct MultiPolygon: Equatable {
+public struct MultiPolygon: Equatable, ForeignMemberContainer {
     /// The positions at which the multipolygon is located. Each nested array corresponds to one polygon.
     public var coordinates: [[[LocationCoordinate2D]]]
 
+    public var foreignMembers: JSONObject = [:]
+
     /// The polygon geometries that conceptually form the multipolygon.
     public var polygons: [Polygon] {
         return coordinates.map { (coordinates) -> Polygon in
@@ -53,12 +55,14 @@ extension MultiPolygon: Codable {
         _ = try container.decode(Kind.self, forKey: .kind)
         let coordinates = try container.decode([[[LocationCoordinate2DCodable]]].self, forKey: .coordinates).decodedCoordinates
         self = .init(coordinates)
+        try decodeForeignMembers(notKeyedBy: CodingKeys.self, with: decoder)
     }
 
     public func encode(to encoder: Encoder) throws {
         var container = encoder.container(keyedBy: CodingKeys.self)
         try container.encode(Kind.MultiPolygon, forKey: .kind)
         try container.encode(coordinates.codableCoordinates, forKey: .coordinates)
+        try encodeForeignMembers(notKeyedBy: CodingKeys.self, to: encoder)
     }
 }
 

Sources/Turf/Geometries/Point.swift

@@ -6,14 +6,16 @@ import CoreLocation
 /**
  A [Point geometry](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.2) represents a single position.
  */
-public struct Point: Equatable {
+public struct Point: Equatable, ForeignMemberContainer {
     /**
      The position at which the point is located.
 
      This property has a plural name for consistency with [RFC 7946](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.2). For convenience, it is represented by a `LocationCoordinate2D` instead of a dedicated `Position` type.
      */
     public var coordinates: LocationCoordinate2D
 
+    public var foreignMembers: JSONObject = [:]
+
     /**
      Initializes a point defined by the given position.
 
@@ -39,11 +41,13 @@ extension Point: Codable {
         _ = try container.decode(Kind.self, forKey: .kind)
         let coordinates = try container.decode(LocationCoordinate2DCodable.self, forKey: .coordinates).decodedCoordinates
         self = .init(coordinates)
+        try decodeForeignMembers(notKeyedBy: CodingKeys.self, with: decoder)
     }
 
     public func encode(to encoder: Encoder) throws {
         var container = encoder.container(keyedBy: CodingKeys.self)
         try container.encode(Kind.Point, forKey: .kind)
         try container.encode(coordinates.codableCoordinates, forKey: .coordinates)
+        try encodeForeignMembers(notKeyedBy: CodingKeys.self, to: encoder)
     }
 }

Sources/Turf/Geometries/Polygon.swift

@@ -6,10 +6,12 @@ import CoreLocation
 /**
  A [Polygon geometry](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.6) is conceptually a collection of `Ring`s that form a single connected geometry.
  */
-public struct Polygon: Equatable {
+public struct Polygon: Equatable, ForeignMemberContainer {
     /// The positions at which the polygon is located. Each nested array corresponds to one linear ring.
     public var coordinates: [[LocationCoordinate2D]]
 
+    public var foreignMembers: JSONObject = [:]
+
     /**
      Initializes a polygon defined by the given positions.
 
@@ -71,12 +73,14 @@ extension Polygon: Codable {
         _ = try container.decode(Kind.self, forKey: .kind)
         let coordinates = try container.decode([[LocationCoordinate2DCodable]].self, forKey: .coordinates).decodedCoordinates
         self = .init(coordinates)
+        try decodeForeignMembers(notKeyedBy: CodingKeys.self, with: decoder)
     }
 
     public func encode(to encoder: Encoder) throws {
         var container = encoder.container(keyedBy: CodingKeys.self)
         try container.encode(Kind.Polygon, forKey: .kind)
         try container.encode(coordinates.codableCoordinates, forKey: .coordinates)
+        try encodeForeignMembers(notKeyedBy: CodingKeys.self, to: encoder)
     }
 }
 

Sources/Turf/Ring.swift

@@ -58,9 +58,7 @@ public struct Ring {
         }
         return area
     }
-}
-
-extension Ring {
+
     /**
      * Determines if the given point falls within the ring.
      * The optional parameter `ignoreBoundary` will result in the method returning true if the given point
@@ -105,3 +103,15 @@ extension Ring {
         return isInside
     }
 }
+
+extension Ring: Codable {
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.singleValueContainer()
+        self = Ring(coordinates: try container.decode([LocationCoordinate2DCodable].self).decodedCoordinates)
+    }
+
+    public func encode(to encoder: Encoder) throws {
+        var container = encoder.singleValueContainer()
+        try container.encode(coordinates.codableCoordinates)
+    }
+}