[swift] Implements union strings (#6589)

5 files changed, 92 insertions, 27 deletions

diff --git a/swift/Sources/FlatBuffers/FlatBufferBuilder.swift b/swift/Sources/FlatBuffers/FlatBufferBuilder.swift
index a868ce10..206603fe 100644
--- a/swift/Sources/FlatBuffers/FlatBufferBuilder.swift
+++ b/swift/Sources/FlatBuffers/FlatBufferBuilder.swift
@@ -28,7 +28,7 @@ public struct FlatBufferBuilder {
   /// A check if the buffer is being written into by a different table
   private var isNested = false
   /// Dictonary that stores a map of all the strings that were written to the buffer
-  private var stringOffsetMap: [String: Offset<String>] = [:]
+  private var stringOffsetMap: [String: Offset] = [:]
   /// A check to see if finish(::) was ever called to retreive data object
   private var finished = false
   /// A check to see if the buffer should serialize Default values
@@ -107,7 +107,7 @@ public struct FlatBufferBuilder {
   /// - Parameters:
   ///   - table: offset for the table
   ///   - fields: Array of all the important fields to be serialized
-  mutating public func require(table: Offset<UOffset>, fields: [Int32]) {
+  mutating public func require(table: Offset, fields: [Int32]) {
     for field in fields {
       let start = _bb.capacity &- Int(table.o)
       let startTable = start &- Int(_bb.read(def: Int32.self, position: start))
@@ -121,7 +121,7 @@ public struct FlatBufferBuilder {
   ///   - offset: Offset of the table
   ///   - fileId: Takes the fileId
   ///   - prefix: if false it wont add the size of the buffer
-  mutating public func finish<T>(offset: Offset<T>, fileId: String, addPrefix prefix: Bool = false) {
+  mutating public func finish(offset: Offset, fileId: String, addPrefix prefix: Bool = false) {
     let size = MemoryLayout<UOffset>.size
     preAlign(len: size &+ (prefix ? size : 0) &+ FileIdLength, alignment: _minAlignment)
     assert(fileId.count == FileIdLength, "Flatbuffers requires file id to be 4")
@@ -133,7 +133,7 @@ public struct FlatBufferBuilder {
   /// - Parameters:
   ///   - offset: Offset of the table
   ///   - prefix: if false it wont add the size of the buffer
-  mutating public func finish<T>(offset: Offset<T>, addPrefix prefix: Bool = false) {
+  mutating public func finish(offset: Offset, addPrefix prefix: Bool = false) {
     notNested()
     let size = MemoryLayout<UOffset>.size
     preAlign(len: size &+ (prefix ? size : 0), alignment: _minAlignment)
@@ -296,7 +296,7 @@ public struct FlatBufferBuilder {
   ///
   /// The current function will fatalError if startVector is called before serializing the vector
   /// - Parameter len: Length of the buffer
-  mutating public func endVector(len: Int) -> Offset<UOffset> {
+  mutating public func endVector(len: Int) -> Offset {
     assert(isNested, "Calling endVector without calling startVector")
     isNested = false
     return Offset(offset: push(element: Int32(len)))
@@ -305,7 +305,7 @@ public struct FlatBufferBuilder {
   /// Creates a vector of type Scalar in the buffer
   /// - Parameter elements: elements to be written into the buffer
   /// - returns: Offset of the vector
-  mutating public func createVector<T: Scalar>(_ elements: [T]) -> Offset<UOffset> {
+  mutating public func createVector<T: Scalar>(_ elements: [T]) -> Offset {
     createVector(elements, size: elements.count)
   }
 
@@ -313,7 +313,7 @@ public struct FlatBufferBuilder {
   /// - Parameter elements: Elements to be written into the buffer
   /// - Parameter size: Count of elements
   /// - returns: Offset of the vector
-  mutating public func createVector<T: Scalar>(_ elements: [T], size: Int) -> Offset<UOffset> {
+  mutating public func createVector<T: Scalar>(_ elements: [T], size: Int) -> Offset {
     let size = size
     startVector(size, elementSize: MemoryLayout<T>.size)
     _bb.push(elements: elements)
@@ -323,7 +323,7 @@ public struct FlatBufferBuilder {
   /// Creates a vector of type Enums in the buffer
   /// - Parameter elements: elements to be written into the buffer
   /// - returns: Offset of the vector
-  mutating public func createVector<T: Enum>(_ elements: [T]) -> Offset<UOffset> {
+  mutating public func createVector<T: Enum>(_ elements: [T]) -> Offset {
     createVector(elements, size: elements.count)
   }
 
@@ -331,7 +331,7 @@ public struct FlatBufferBuilder {
   /// - Parameter elements: Elements to be written into the buffer
   /// - Parameter size: Count of elements
   /// - returns: Offset of the vector
-  mutating public func createVector<T: Enum>(_ elements: [T], size: Int) -> Offset<UOffset> {
+  mutating public func createVector<T: Enum>(_ elements: [T], size: Int) -> Offset {
     let size = size
     startVector(size, elementSize: T.byteSize)
     for e in elements.reversed() {
@@ -343,7 +343,7 @@ public struct FlatBufferBuilder {
   /// Creates a vector of type Offsets  in the buffer
   /// - Parameter offsets:Array of offsets of type T
   /// - returns: Offset of the vector
-  mutating public func createVector<T>(ofOffsets offsets: [Offset<T>]) -> Offset<UOffset> {
+  mutating public func createVector(ofOffsets offsets: [Offset]) -> Offset {
     createVector(ofOffsets: offsets, len: offsets.count)
   }
 
@@ -351,8 +351,8 @@ public struct FlatBufferBuilder {
   /// - Parameter elements: Array of offsets of type T
   /// - Parameter size: Count of elements
   /// - returns: Offset of the vector
-  mutating public func createVector<T>(ofOffsets offsets: [Offset<T>], len: Int) -> Offset<UOffset> {
-    startVector(len, elementSize: MemoryLayout<Offset<T>>.size)
+  mutating public func createVector(ofOffsets offsets: [Offset], len: Int) -> Offset {
+    startVector(len, elementSize: MemoryLayout<Offset>.size)
     for o in offsets.reversed() {
       push(element: o)
     }
@@ -362,8 +362,8 @@ public struct FlatBufferBuilder {
   /// Creates a vector of Strings
   /// - Parameter str: a vector of strings that will be written into the buffer
   /// - returns: Offset of the vector
-  mutating public func createVector(ofStrings str: [String]) -> Offset<UOffset> {
-    var offsets: [Offset<String>] = []
+  mutating public func createVector(ofStrings str: [String]) -> Offset {
+    var offsets: [Offset] = []
     for s in str {
       offsets.append(create(string: s))
     }
@@ -373,7 +373,7 @@ public struct FlatBufferBuilder {
   /// Creates a vector of `Native swift structs` which were padded to flatbuffers standards
   /// - Parameter structs: A vector of structs
   /// - Returns: offset of the vector
-  mutating public func createVector<T: NativeStruct>(ofStructs structs: [T]) -> Offset<UOffset> {
+  mutating public func createVector<T: NativeStruct>(ofStructs structs: [T]) -> Offset {
     startVector(structs.count * MemoryLayout<T>.size, elementSize: MemoryLayout<T>.alignment)
     for i in structs.reversed() {
       _ = create(struct: i)
@@ -390,7 +390,7 @@ public struct FlatBufferBuilder {
   /// - Returns: offset of written struct
   @discardableResult
   mutating public func create<T: NativeStruct>(
-    struct s: T, position: VOffset) -> Offset<UOffset>
+    struct s: T, position: VOffset) -> Offset
   {
     let offset = create(struct: s)
     _vtableStorage.add(loc: FieldLoc(offset: _bb.size, position: VOffset(position)))
@@ -403,7 +403,7 @@ public struct FlatBufferBuilder {
   /// - Returns: offset of written struct
   @discardableResult
   mutating public func create<T: NativeStruct>(
-    struct s: T) -> Offset<UOffset>
+    struct s: T) -> Offset
   {
     let size = MemoryLayout<T>.size
     preAlign(len: size, alignment: MemoryLayout<T>.alignment)
@@ -416,7 +416,7 @@ public struct FlatBufferBuilder {
   /// Insets a string into the buffer using UTF8
   /// - Parameter str: String to be serialized
   /// - returns: The strings offset in the buffer
-  mutating public func create(string str: String?) -> Offset<String> {
+  mutating public func create(string str: String?) -> Offset {
     guard let str = str else { return Offset() }
     let len = str.utf8.count
     notNested()
@@ -432,7 +432,7 @@ public struct FlatBufferBuilder {
   /// The function checks the stringOffsetmap if it's seen a similar string before
   /// - Parameter str: String to be serialized
   /// - returns: The strings offset in the buffer
-  mutating public func createShared(string str: String?) -> Offset<String> {
+  mutating public func createShared(string str: String?) -> Offset {
     guard let str = str else { return Offset() }
     if let offset = stringOffsetMap[str] {
       return offset
@@ -448,7 +448,7 @@ public struct FlatBufferBuilder {
   /// - Parameters:
   ///   - offset: Offset of another object to be written
   ///   - position: The  predefined position of the object
-  mutating public func add<T>(offset: Offset<T>, at position: VOffset) {
+  mutating public func add(offset: Offset, at position: VOffset) {
     if offset.isEmpty { return }
     add(element: refer(to: offset.o), def: 0, at: position)
   }
@@ -457,7 +457,7 @@ public struct FlatBufferBuilder {
   /// - Parameter o: Offset
   /// - returns: Position of the offset
   @discardableResult
-  mutating public func push<T>(element o: Offset<T>) -> UOffset {
+  mutating public func push(element o: Offset) -> UOffset {
     push(element: refer(to: o.o))
   }
 
diff --git a/swift/Sources/FlatBuffers/FlatBufferObject.swift b/swift/Sources/FlatBuffers/FlatBufferObject.swift
index c3f1713c..72325e79 100644
--- a/swift/Sources/FlatBuffers/FlatBufferObject.swift
+++ b/swift/Sources/FlatBuffers/FlatBufferObject.swift
@@ -20,15 +20,21 @@ import Foundation
 /// since now we will be serializing native structs into the buffer.
 public protocol NativeStruct {}
 
+/// FlatbuffersInitializable is a protocol that allows any object to be
+/// Initialized from a ByteBuffer
+public protocol FlatbuffersInitializable {
+  init(_ bb: ByteBuffer, o: Int32)
+}
+
 /// FlatbufferObject structures all the Flatbuffers objects
-public protocol FlatBufferObject {
+public protocol FlatBufferObject: FlatbuffersInitializable {
   var __buffer: ByteBuffer! { get }
-  init(_ bb: ByteBuffer, o: Int32)
 }
 
 public protocol ObjectAPIPacker {
   associatedtype T
-  static func pack(_ builder: inout FlatBufferBuilder, obj: inout T) -> Offset<UOffset>
+  static func pack(_ builder: inout FlatBufferBuilder, obj: inout T?) -> Offset
+  static func pack(_ builder: inout FlatBufferBuilder, obj: inout T) -> Offset
   mutating func unpack() -> T
 }
 
diff --git a/swift/Sources/FlatBuffers/Offset.swift b/swift/Sources/FlatBuffers/Offset.swift
index abf489b1..bd3f8a86 100644
--- a/swift/Sources/FlatBuffers/Offset.swift
+++ b/swift/Sources/FlatBuffers/Offset.swift
@@ -17,7 +17,7 @@
 import Foundation
 
 /// Offset object for all the Objects that are written into the buffer
-public struct Offset<T> {
+public struct Offset {
   /// Offset of the object in the buffer
   public var o: UOffset
   /// Returns false if the offset is equal to zero
diff --git a/swift/Sources/FlatBuffers/String+extension.swift b/swift/Sources/FlatBuffers/String+extension.swift
new file mode 100644
index 00000000..7c9b06e7
--- /dev/null
+++ b/swift/Sources/FlatBuffers/String+extension.swift
@@ -0,0 +1,59 @@
+/*
+ * Copyright 2021 Google Inc. All rights reserved.
+ *
+ * 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.
+ */
+
+import Foundation
+
+extension String: FlatbuffersInitializable {
+
+  /// Initailizes a string from a Flatbuffers ByteBuffer
+  /// - Parameters:
+  ///   - bb: ByteBuffer containing the readable string
+  ///   - o: Current position
+  public init(_ bb: ByteBuffer, o: Int32) {
+    let count = bb.read(def: Int32.self, position: Int(o))
+    self = bb.readString(
+      at: Int32(MemoryLayout<Int32>.size) + o,
+      count: count) ?? ""
+  }
+}
+
+extension String: ObjectAPIPacker {
+
+  public static func pack(_ builder: inout FlatBufferBuilder, obj: inout String?) -> Offset {
+    guard var obj = obj else { return Offset() }
+    return pack(&builder, obj: &obj)
+  }
+
+  public static func pack(_ builder: inout FlatBufferBuilder, obj: inout String) -> Offset {
+    builder.create(string: obj)
+  }
+
+  public mutating func unpack() -> String {
+    self
+  }
+
+}
+
+extension String: NativeObject {
+
+  public func serialize<T: ObjectAPIPacker>(type: T.Type) -> ByteBuffer where T.T == Self {
+    fatalError("serialize should never be called from string directly")
+  }
+
+  public func serialize<T: ObjectAPIPacker>(builder: inout FlatBufferBuilder, type: T.Type) -> ByteBuffer where T.T == Self {
+    fatalError("serialize should never be called from string directly")
+  }
+}
diff --git a/swift/Sources/FlatBuffers/Table.swift b/swift/Sources/FlatBuffers/Table.swift
index dc711be4..e5842aa1 100644
--- a/swift/Sources/FlatBuffers/Table.swift
+++ b/swift/Sources/FlatBuffers/Table.swift
@@ -80,12 +80,12 @@ public struct Table {
     return r
   }
 
-  public func union<T: FlatBufferObject>(_ o: Int32) -> T {
+  public func union<T: FlatbuffersInitializable>(_ o: Int32) -> T {
     let o = o + postion
     return directUnion(o)
   }
 
-  public func directUnion<T: FlatBufferObject>(_ o: Int32) -> T {
+  public func directUnion<T: FlatbuffersInitializable>(_ o: Int32) -> T {
     T.init(bb, o: o + bb.read(def: Int32.self, position: Int(o)))
   }