The relationship between Scala Future components
As we know, the Scala Future API is used to write asynchronous programs. It has three main components—Future, Promise, and ExecutionContext.
Let's discuss the relationship and differences between these components. The following diagram shows how the Scala Future API components work together:
As shown in the preceding diagram, Future[T] contains a computation task of type T. Promise[T] executes that computation task T in ExecutionContext and writes the results back into the Future[T].
Differences between a Future and a Promise
In Scala, a Future and a Promise have the following differences:
- A Promise is used to compute a value, whereas a Future is used to read that value
- A Promise is used write the value, whereas a Future is a read-only object
- Once a Promise is completed, we cannot change its value, it becomes immutable
- Once a Future is completed, we cannot change its value, it becomes immutable
- A Future is for querying data and a Promise is for writing...
