IO[E, A] is a type alias for
ZIO[Any, E, A], which represents an effect that has no requirements, and may fail with an
E, or succeed with an
In Scala, the type alias is a way to give a name to another type, to avoid having to repeat the original type again and again. It doesn't affect the type-checking process. It just helps us to have an expressive API design.
Let's see how the
IO type alias is defined:
type IO[+E, +A] = ZIO[Any, E, A]
IO just equal to
ZIO which doesn't need any requirement.
ZIO values of type
IO[E, Nothing] (where the value type is
Nothing) are considered unproductive, because the
Nothing type is uninhabitable, i.e. there can be no actual values of type
Nothing. Values of this type may fail with an
E, but will never produce a value.
Note: Principle of The Least Power
ZIOdata type is the most powerful effect in the ZIO library. It helps us to model various types of workflows. On other hand, the type aliases are a way of subtyping and specializing the
ZIOtype, specific for a less powerful workflow.
Lot of the time, we don't need such a piece of powerful machinery. So as a rule of thumb, whenever we require a less powerful effect, it's better to use the proper specialized type alias.
So there is no need to convert type aliases to the
ZIOdata type, whenever the
ZIOdata type is required, we can use the most precise type alias to fit our workflow requirement.