Asynchronous Operations: Async Vs. Awaitable

Why is the async keyword needed for functions that return Awaitable? Because it is possible to have non-async functions that return awaitables; the async keyword is merely an implementation detail. For this reason, async is not allowed in interfaces. For example:

interface Car {
  // It doesn't matter to the caller how this is implemented, only that it
  // returns an Awaitable<void>
  public function drive(): Awaitable<void>;

This can be implemented with an async function, like this:

class Ford implements Car {
  public async function drive(): Awaitable<void> {
    // ...

It can also be implemented by a non-async function, like this:

class VolkswagenDiesel implements Car {
  public function drive(): Awaitable<void> {
    // ...
    return $this->driveNormally();
  private async function driveNormally(): Awaitable<void> {
    // ...

The use of async is strongly encouraged for all functions, except for:

  • Interface method declarations
  • Abstract method declarations

The async keyword should be used in most other cases, including implementations of interface or abstract methods.

Was This Page Useful?
Thank You!
Thank You! If you'd like to share more feedback, please file an issue.