ZManaged

ZManaged is a data type in the ZIO ecosystem that represents a resource with an explicit lifecycle. It encapsulates the actions to acquire a resource along with a release or finalization action, ensuring that the resource is released when it is no longer in use, even in the face of errors or interruptions. ZManaged is parameterized as ZManaged[R, E, A], where R is the required environment, E is the error type, and A is the resource type.

The core idea is to separate acquisition from release and to compose resource lifecycles in a safe, deterministic way. A ZManaged value describes how to obtain an A from an environment R and how to release A afterward. Rather than performing acquisition and cleanup in a single effect, ZManaged provides a structured way to compose multiple resources and manage their lifetimes. The primary operation for using a ZManaged is a scoped “use” (or equivalent) that runs a function with the acquired resource and guarantees the release action will run after the function completes, regardless of success or failure.

ZManaged offers constructors and combinators to build and transform resources. You can create a managed from a pair of acquisition and release actions, lift ordinary effects into managed context, and transform or map the resource. It can also be combined with other managed resources to form composite lifecycles, releasing resources in a well-defined order.

Common use cases include managing database connections, file handles, sockets, and thread pools. By providing guarantees about finalization, ZManaged helps prevent resource leaks and simplifies error handling in effectful programs.

See also: ZIO, resource safety, managed resources.