Before you get started

Before diving into the FlatBuffers usage in Swift, it should be noted that the Tutorial page has a complete guide to general FlatBuffers usage in all of the supported languages (including Swift). This page is designed to cover the nuances of FlatBuffers usage, specific to Swift.

You should also have read the Building documentation to build flatc and should be familiar with Using the schema compiler and Writing a schema.

FlatBuffers Swift library code location

The code for the FlatBuffers Swift library can be found at flatbuffers/swift. You can browse the library code on the FlatBuffers GitHub page.

Testing the FlatBuffers Swift library

The code to test the Swift library can be found at flatbuffers/Flatbuffers.Test.Swift. The test code itself is located in Flatbuffers.Test.Swift.

To run the tests, use the SwiftTest.sh shell script.

Note: The shell script requires Swift to be installed.

Using the FlatBuffers Swift library

Note: See Tutorial for a more in-depth example of how to use FlatBuffers in Swift.

FlatBuffers supports reading and writing binary FlatBuffers in Swift.

To use FlatBuffers in your own code, first generate Swift structs from your schema with the --swift option to flatc. Then include FlatBuffers using SPM in by adding the path to FlatBuffers/swift into it. The generated code should also be added to xcode or the path of the package you will be using. Note: sometimes xcode cant and wont see the generated files, so it's better that you copy them to xcode.

For example, here is how you would read a FlatBuffer binary file in Swift: First, include the library and copy thegenerated code. Then read a FlatBuffer binary file or a data object from the server, which you can pass into the GetRootAsMonster function.

import FlatBuffers
 
typealias Monster1 = MyGame.Sample.Monster
typealias Vec3 = MyGame.Sample.Vec3
 
let path = FileManager.default.currentDirectoryPath
let url = URL(fileURLWithPath: path, isDirectory: true).appendingPathComponent("monsterdata_test").appendingPathExtension("mon")
guard let data = try? Data(contentsOf: url) else { return }
 
let monster = Monster.getRootAsMonster(bb: ByteBuffer(data: data))

Now you can access values like this:

let hp = monster.hp
let pos = monster.pos // uses native swift structs
let pos = monster.mutablePos // uses flatbuffers structs

In some cases it's necessary to modify values in an existing FlatBuffer in place (without creating a copy). For this reason, scalar fields of a Flatbuffer table or struct can be mutated.

let monster = Monster.getRootAsMonster(bb: ByteBuffer(data: data))
 
if !monster.mutate(hp: 10) {
  fatalError("couldn't mutate")
}
// mutate a struct field using flatbuffers struct
// DONT use monster.pos to mutate since swift copy on write 
// will not mutate the value in the buffer
let vec = monster.mutablePos.mutate(z: 4)
 
// This mutation will fail because the mana field is not available in
// the buffer. It should be set when creating the buffer.
if !monster.mutate(mana: 20) {
  fatalError("couldn't mutate")
}

The term mutate is used instead of set to indicate that this is a special use case. All mutate functions return a boolean value which is false if the field we're trying to mutate is not available in the buffer.