Introduction

ZIO contains a few data types that can help you solve complex problems in asynchronous and concurrent programming. ZIO data types categorize into these sections:

1. Core Data Types
2. Contextual Data Types
3. Concurrency
   • Fiber Primitives
   • Concurrency Primitives
   • Synchronization Aids
   • STM
4. Resource Management
5. Streaming
6. Miscellaneous

Core Data Types

• ZIO — A ZIO is a value that models an effectful program, which might fail or succeed.
  • UIO — An UIO[A] is a type alias for ZIO[Any, Nothing, A].
  • URIO — An URIO[R, A] is a type alias for ZIO[R, Nothing, A].
  • Task — A Task[A] is a type alias for ZIO[Any, Throwable, A].
  • RIO — A RIO[R, A] is a type alias for ZIO[R, Throwable, A].
  • IO — An IO[E, A] is a type alias for ZIO[Any, E, A].
• Exit — An Exit[E, A] describes the result of executing an IO value.
• Cause - Cause[E] is a description of a full story of a fiber failure.
• Runtime — A Runtime[R] is capable of executing tasks within an environment R.

Contextual Data Types

• Has — The trait Has[A] is used with the ZIO environment to express an effect's dependency on a service of type A.
• ZLayer — The ZIO[-R, +E, +A] data type describes an effect that requires an input type of R, as an environment, may fail with an error of type E or succeed and produces a value of type A.
  • RLayer — RLayer[-RIn, +ROut] is a type alias for ZLayer[RIn, Throwable, ROut], which represents a layer that requires RIn as its input, it may fail with Throwable value, or returns ROut as its output.
  • ULayer — ULayer[+ROut] is a type alias for ZLayer[Any, Nothing, ROut], which represents a layer that doesn't require any services as its input, it can't fail, and returns ROut as its output.
  • Layer — Layer[+E, +ROut] is a type alias for ZLayer[Any, E, ROut], which represents a layer that doesn't require any services, it may fail with an error type of E, and returns ROut as its output.
  • URLayer — URLayer[-RIn, +ROut] is a type alias for ZLayer[RIn, Nothing, ROut], which represents a layer that requires RIn as its input, it can't fail, and returns ROut as its output.
  • TaskLayer — TaskLayer[+ROut] is a type alias for ZLayer[Any, Throwable, ROut], which represents a layer that doesn't require any services as its input, it may fail with Throwable value, and returns ROut as its output.

Concurrency

Fiber Primitives

• Fiber — A fiber value models an IO value that has started running, and is the moral equivalent of a green thread.
• FiberRef — FiberRef[A] models a mutable reference to a value of type A. As opposed to Ref[A], a value is bound to an executing Fiber only. You can think of it as Java's ThreadLocal on steroids.
• Fiber.Status — Fiber.Status describe the current status of a Fiber.
• Fiber.Id — Fiber.Id describe the unique identity of a Fiber.

Concurrency Primitives

• Hub - A Hub is an asynchronous message hub that allows publishers to efficiently broadcast values to many subscribers.
• Promise — A Promise is a model of a variable that may be set a single time, and awaited on by many fibers.
• Semaphore — A Semaphore is an asynchronous (non-blocking) semaphore that plays well with ZIO's interruption.
• ZRef — A ZRef[EA, EB, A, B] is a polymorphic, purely functional description of a mutable reference. The fundamental operations of a ZRef are set and get.
  • Ref — Ref[A] models a mutable reference to a value of type A. The two basic operations are set, which fills the Ref with a new value, and get, which retrieves its current content. All operations on a Ref are atomic and thread-safe, providing a reliable foundation for synchronizing concurrent programs.
• ZRefM — A ZRefM[RA, RB, EA, EB, A, B] is a polymorphic, purely functional description of a mutable reference.
  • RefM — RefM[A] models a mutable reference to a value of type A in which we can store immutable data, and update it atomically and effectfully.
• Queue — A Queue is an asynchronous queue that never blocks, which is safe for multiple concurrent producers and consumers.

Synchronization aids

• ConcurrentMap — A Map wrapper over java.util.concurrent.ConcurrentHashMap
• ConcurrentSet — A Set implementation over java.util.concurrent.ConcurrentHashMap
• CountdownLatch — A synchronization aid that allows one or more fibers to wait until a set of operations being performed in other fibers completes.
• CyclicBarrier — A synchronization aid that allows a set of fibers to all wait for each other to reach a common barrier point.

STM

• STM - An STM represents an effect that can be performed transactionally resulting in a failure or success.
• TArray - A TArray is an array of mutable references that can participate in transactions.
• TSet - A TSet is a mutable set that can participate in transactions.
• TMap - A TMap is a mutable map that can participate in transactions.
• TRef - A TRef is a mutable reference to an immutable value that can participate in transactions.
• TPriorityQueue - A TPriorityQueue is a mutable priority queue that can participate in transactions.
• TPromise - A TPromise is a mutable reference that can be set exactly once and can participate in transactions.
• TQueue - A TQueue is a mutable queue that can participate in transactions.
• TReentrantLock - A TReentrantLock is a reentrant read / write lock that can be composed.
• TSemaphore - A TSemaphore is a semaphore that can participate in transactions.

Resource Management

• Managed — A Managed is a value that describes a perishable resource that may be consumed only once inside a given scope.

Streaming

The following datatypes can be found in ZIO streams library:

• ZStream — A ZStream is a lazy, concurrent, asynchronous source of values.
• ZSink — A ZSink is a consumer of values from a ZStream, which may produces a value when it has consumed enough.

Miscellaneous

• Chunk — ZIO Chunk: Fast, Pure Alternative to Arrays
• Schedule — A Schedule is a model of a recurring schedule, which can be used for repeating successful IO values, or retrying failed IO values.

To learn more about these data types, please explore the pages above, or check out the Scaladoc documentation.