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Using Fiber

What is Fiber?​

Ruby provides a class called Fiber for working with coroutines.

A coroutine is a mechanism that allows you to pause execution and later resume it from where it left off.

In some languages, asynchronous operation using async/await are referred to as coroutines. However, Ruby's Fiber uses yield and resume to pause and resume execution.

To create a Fiber, use Fiber.new.

Note that simply calling Fiber.new does not start execution. Let's try it out using the REPL.

@fiber = Fiber.new do
  Godot.emit_signal :fiber, 'started'
  Fiber.yield
  Godot.emit_signal :fiber, 'resumed'
end
Output
=> "#<Fiber:0x1ab31c76030 (created)>"

To start execution, call resume.

@fiber.resume
Output
[ fiber ] signal emitted: 'started'
=> <null>

When Fiber.yield is called, execution is paused at that point. To resume, call resume again.

@fiber.resume
Output
[ fiber ] signal emitted: 'resumed'
=> true

Fiber.yield Arguments and Return Values​

The arguments passed to Fiber.yield will be returned when resume is called.

@fiber = Fiber.new do
  value = Fiber.yield 'started'
  Godot.emit_signal :fiber, value
end
@fiber.resume
Output
=> "started"

The arguments passed to resume become the return values of Fiber.yield.

@fiber.resume 'hello'
Output
[ fiber ] signal emitted: "hello"
=> true

By using coroutines, you can pause and resume execution at arbitary points—making it possible to build systems like a dialogue system.

In the next chapter, we'll build a dialogue system example using Fiber.