The way Roblox models asynchronous operations by default is by yielding (stopping) the thread and then resuming it when the future value is available. This model is not ideal because:
- Functions you call can yield without warning, or only yield sometimes, leading to unpredictable and surprising results. Accidentally yielding the thread is the source of a large class of bugs and race conditions that Roblox developers run into.
- It is difficult to deal with running multiple asynchronous operations concurrently and then retrieve all of their values at the end without extraneous machinery.
- When an asynchronous operation fails or an error is encountered, Lua functions usually either raise an error or return a success value followed by the actual value. Both of these methods lead to repeating the same tired patterns many times over for checking if the operation was successful.
- Yielding lacks easy access to introspection and the ability to cancel an operation if the value is no longer needed.
This Promise implementation attempts to satisfy these traits:
- An object that represents a unit of asynchronous work
- Composability
- Predictable timing