zio

Evidence type A is not equal to type B.

A simple, macro-less means of creating accessors from Services. Extend the companion object with Accessible[ServiceName], then simply call Companion(_.someMethod), to return a ZIO effect that requires the Service in its environment.

Example:

 trait FooService {
   def magicNumber: UIO[Int]
   def castSpell(chant: String): UIO[Boolean]
 }

 object FooService extends Accessible[FooService]

 val example: ZIO[Has[FooService], Nothing, Unit] =
   for {
     int  <- FooService(_.magicNumber)
     bool <- FooService(_.castSpell("Oogabooga!"))
   } yield ()

The entry point for a purely-functional application on the JVM.

import zio.App
import zio.console._

object MyApp extends App {

 final def run(args: List[String]) =
   myAppLogic.exitCode

 def myAppLogic =
   for {
     _ <- putStrLn("Hello! What is your name?")
     n <- getStrLn
     _ <- putStrLn("Hello, " + n + ", good to meet you!")
   } yield ()
}

This object was generated by sbt-buildinfo.

A value of type CanFail[E] provides implicit evidence that an effect with error type E can fail, that is, that E is not equal to Nothing.

A Chunk[A] represents a chunk of values of type A. Chunks are designed are usually backed by arrays, but expose a purely functional, safe interface to the underlying elements, and they become lazy on operations that would be costly with arrays, such as repeated concatenation.

The implementation of balanced concatenation is based on the one for Conc-Trees in "Conc-Trees for Functional and Parallel Programming" by Aleksandar Prokopec and Martin Odersky. http://aleksandar-prokopec.com/resources/docs/lcpc-conc-trees.pdf

NOTE: For performance reasons Chunk does not box primitive types. As a result, it is not safe to construct chunks from heterogeneous primitive types.

A ChunkBuilder[A] can build a Chunk[A] given elements of type A. ChunkBuilder is a mutable data structure that is implemented to efficiently build chunks of unboxed primitives and for compatibility with the Scala collection library.

ChunkLike represents the capability for a Chunk to extend Scala's collection library. Because of changes to Scala's collection library in 2.13, separate versions of this trait are implemented for 2.11 / 2.12 and 2.13 / Dotty. This allows code in Chunk to be written without concern for the implementation details of Scala's collection library to the maximum extent possible.

Note that IndexedSeq is not a referentially transparent interface in that it exposes methods that are partial (e.g. apply), allocate mutable state (e.g. iterator), or are purely side effecting (e.g. foreach). Chunk extends IndexedSeq to provide interoperability with Scala's collection library but users should avoid these methods whenever possible.

Describes a strategy for evaluating multiple effects, potentially in parallel. There are three possible execution strategies: Sequential, Parallel, and ParallelN.

An Exit[E, A] describes the result of executing an IO value. The result is either succeeded with a value A, or failed with a Cause[E].

A fiber is a lightweight thread of execution that never consumes more than a whole thread (but may consume much less, depending on contention and asynchronicity). Fibers are spawned by forking ZIO effects, which run concurrently with the parent effect.

Fibers can be joined, yielding their result to other fibers, or interrupted, which terminates the fiber, safely releasing all resources.

def parallel[A, B](io1: Task[A], io2: Task[B]): Task[(A, B)] =
 for {
   fiber1 <- io1.fork
   fiber2 <- io2.fork
   a      <- fiber1.join
   b      <- fiber2.join
 } yield (a, b)

Represents a failure in a fiber. This could be caused by some non- recoverable error, such as a defect or system error, by some typed error, or by interruption (or combinations of all of the above).

This class is used to wrap ZIO failures into something that can be thrown, to better integrate with Scala exception handling.

Fiber's counterpart for Java's ThreadLocal. Value is automatically propagated to child on fork and merged back in after joining child.

for {
 fiberRef <- FiberRef.make("Hello world!")
 child <- fiberRef.set("Hi!).fork
 result <- child.join
} yield result

result will be equal to "Hi!" as changes done by child were merged on join.

FiberRef#make also allows specifying how the values will be combined when joining. By default this will use the value of the joined fiber.

for {
 fiberRef <- FiberRef.make(0, math.max)
 child    <- fiberRef.update(_ + 1).fork
 _        <- fiberRef.update(_ + 2)
 _        <- child.join
 value    <- fiberRef.get
} yield value

value will be 2 as the value in the joined fiber is lower and we specified max as our combine function.

The trait Has[A] is used with ZIO environment to express an effect's dependency on a service of type A. For example, RIO[Has[Console.Service], Unit] is an effect that requires a Console.Service service. Inside the ZIO library, type aliases are provided as shorthands for common services, e.g.:

type Console = Has[ConsoleService]

Services parameterized on path dependent types are not supported.

The InterruptStatus of a fiber determines whether or not it can be interrupted. The status can change over time in different regions.

A value of type NeedsEnv[R] provides implicit evidence that an effect with environment type R needs an environment, that is, that R is not equal to Any.

A NonEmptyChunk is a Chunk that is guaranteed to contain at least one element. As a result, operations which would not be safe when performed on Chunk, such as head or reduce, are safe when performed on NonEmptyChunk. Operations on NonEmptyChunk which could potentially return an empty chunk will return a Chunk instead.

A promise represents an asynchronous variable, of zio.IO type, that can be set exactly once, with the ability for an arbitrary number of fibers to suspend (by calling await) and automatically resume when the variable is set.

Promises can be used for building primitive actions whose completions require the coordinated action of multiple fibers, and for building higher-level concurrent or asynchronous structures.

for {
 promise <- Promise.make[Nothing, Int]
 _       <- promise.succeed(42).delay(1.second).fork
 value   <- promise.await // Resumes when forked fiber completes promise
} yield value

A Reservation[-R, +E, +A] encapsulates resource acquisition and disposal without specifying when or how that resource might be used.

See ZManaged#reserve and ZIO#reserve for details of usage.

A Runtime[R] is capable of executing tasks within an environment R.

A Schedule[Env, In, Out] defines a recurring schedule, which consumes values of type In, and which returns values of type Out.

Schedules are defined as a possibly infinite set of intervals spread out over time. Each interval defines a window in which recurrence is possible.

When schedules are used to repeat or retry effects, the starting boundary of each interval produced by a schedule is used as the moment when the effect will be executed again.

Schedules compose in the following primary ways:

• Union. This performs the union of the intervals of two schedules. * Intersection. This performs the intersection of the intervals of two schedules. * Sequence. This concatenates the intervals of one schedule onto another.

In addition, schedule inputs and outputs can be transformed, filtered (to terminate a schedule early in response to some input or output), and so forth.

A variety of other operators exist for transforming and combining schedules, and the companion object for Schedule contains all common types of schedules, both for performing retrying, as well as performing repetition.

An asynchronous semaphore, which is a generalization of a mutex. Semaphores have a certain number of permits, which can be held and released concurrently by different parties. Attempts to acquire more permits than available result in the acquiring fiber being suspended until the specified number of permits become available.

A Supervisor[A] is allowed to supervise the launching and termination of fibers, producing some visible value of type A from the supervision.

Whether ZIO Tracing is enabled for the current fiber in the current region.

A ZHub[RA, RB, EA, EB, A, B] is an asynchronous message hub. Publishers can publish messages of type A to the hub and subscribers can subscribe to take messages of type B from the hub. Publishing messages can require an environment of type RA and fail with an error of type EA. Taking messages can require an environment of type RB and fail with an error of type EB.

A ZIO[R, E, A] value is an immutable value that lazily describes a workflow or job. The workflow requires some environment R, and may fail with an error of type E, or succeed with a value of type A.

These lazy workflows, referred to as effects, can be informally thought of as functions in the form:

R => Either[E, A]

ZIO effects model resourceful interaction with the outside world, including synchronous, asynchronous, concurrent, and parallel interaction.

ZIO effects use a fiber-based concurrency model, with built-in support for scheduling, fine-grained interruption, structured concurrency, and high scalability.

To run an effect, you need a Runtime, which is capable of executing effects. Runtimes bundle a thread pool together with the environment that effects need.

A ZLayer[A, E, B] describes a layer of an application: every layer in an application requires some services (the input) and produces some services (the output).

Layers can be thought of as recipes for producing bundles of services, given their dependencies (other services).

Construction of layers can be effectful and utilize resources that must be acquired and safely released when the services are done being utilized.

By default layers are shared, meaning that if the same layer is used twice the layer will only be allocated a single time.

Because of their excellent composition properties, layers are the idiomatic way in ZIO to create services that depend on other services.

A ZManaged[R, E, A] is a managed resource of type A, which may be used by invoking the use method of the resource. The resource will be automatically acquired before the resource is used, and automatically released after the resource is used.

Resources do not survive the scope of use, meaning that if you attempt to capture the resource, leak it from use, and then use it after the resource has been consumed, the resource will not be valid anymore and may fail with some checked error, as per the type of the functions provided by the resource.

A ZPool[E, A] is a pool of items of type A, each of which may be associated with the acquisition and release of resources. An attempt to get an item A from a pool may fail with an error of type E.

A ZQueue[RA, RB, EA, EB, A, B] is a lightweight, asynchronous queue into which values of type A can be enqueued and of which elements of type B can be dequeued. The queue's enqueueing operations may utilize an environment of type RA and may fail with errors of type EA. The dequeueing operations may utilize an environment of type RB and may fail with errors of type EB.

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. set takes a value of type A and sets the reference to a new value, potentially failing with an error of type EA. get gets the current value of the reference and returns a value of type B, potentially failing with an error of type EB.

When the error and value types of the ZRef are unified, that is, it is a ZRef[E, E, A, A], the ZRef also supports atomic modify and update operations. All operations are guaranteed to be safe for concurrent access.

NOTE: While ZRef provides the functional equivalent of a mutable reference, the value inside the ZRef should be immutable. For performance reasons ZRef is implemented in terms of compare and swap operations rather than synchronization. These operations are not safe for mutable values that do not support concurrent access.

A ZRefM[RA, RB, EA, EB, A, B] is a polymorphic, purely functional description of a mutable reference. The fundamental operations of a ZRefM are set and get. set takes a value of type A and sets the reference to a new value, requiring an environment of type RA and potentially failing with an error of type EA. get gets the current value of the reference and returns a value of type B, requiring an environment of type RB and potentially failing with an error of type EB.

When the error and value types of the ZRefM are unified, that is, it is a ZRefM[E, E, A, A], the ZRefM also supports atomic modify and update operations.

Unlike ZRef, ZRefM allows performing effects within update operations, at some cost to performance. Writes will semantically block other writers, while multiple readers can read simultaneously.

A ZScope[A] is a value that allows adding finalizers identified by a key. Scopes are closed with a value of type A, which is provided to all the finalizers when the scope is released.

For safety reasons, this interface has no method to close a scope. Rather, an open scope may be required with ZScope.make, which returns a function that can close a scope. This allows scopes to be safely passed around without fear they will be accidentally closed.

A queue that can only be dequeued.

A queue that can only be enqueued.