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Pods/FirebaseFirestore/Firestore/Swift/Source/Codable/ExplicitNull.swift

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+/*
+ * Copyright 2019 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if SWIFT_PACKAGE
+  @_exported import FirebaseFirestoreInternalWrapper
+#else
+  @_exported import FirebaseFirestoreInternal
+#endif // SWIFT_PACKAGE
+
+/// Wraps an `Optional` field in a `Codable` object such that when the field
+/// has a `nil` value it will encode to a null value in Firestore. Normally,
+/// optional fields are omitted from the encoded document.
+///
+/// This is useful for ensuring a field is present in a Firestore document,
+/// even when there is no associated value.
+@propertyWrapper
+public struct ExplicitNull<Value> {
+  var value: Value?
+
+  public init(wrappedValue value: Value?) {
+    self.value = value
+  }
+
+  public var wrappedValue: Value? {
+    get { value }
+    set { value = newValue }
+  }
+}
+
+extension ExplicitNull: Equatable where Value: Equatable {}
+
+extension ExplicitNull: Hashable where Value: Hashable {}
+
+extension ExplicitNull: Encodable where Value: Encodable {
+  public func encode(to encoder: Encoder) throws {
+    var container = encoder.singleValueContainer()
+    if let value = value {
+      try container.encode(value)
+    } else {
+      try container.encodeNil()
+    }
+  }
+}
+
+extension ExplicitNull: Decodable where Value: Decodable {
+  public init(from decoder: Decoder) throws {
+    let container = try decoder.singleValueContainer()
+    if container.decodeNil() {
+      value = nil
+    } else {
+      value = try container.decode(Value.self)
+    }
+  }
+}