| /* |
| * |
| * Copyright 2015, Google Inc. |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions are |
| * met: |
| * |
| * * Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * * Redistributions in binary form must reproduce the above |
| * copyright notice, this list of conditions and the following disclaimer |
| * in the documentation and/or other materials provided with the |
| * distribution. |
| * * Neither the name of Google Inc. nor the names of its |
| * contributors may be used to endorse or promote products derived from |
| * this software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| * |
| */ |
| |
| #import <Foundation/Foundation.h> |
| |
| #import "GRXWriteable.h" |
| |
| typedef NS_ENUM(NSInteger, GRXWriterState) { |
| |
| // The writer has not yet been given a writeable to which it can push its |
| // values. To have an writer transition to the Started state, send it a |
| // startWithWriteable: message. |
| // |
| // An writer's state cannot be manually set to this value. |
| GRXWriterStateNotStarted, |
| |
| // The writer might push values to the writeable at any moment. |
| GRXWriterStateStarted, |
| |
| // The writer is temporarily paused, and won't send any more values to the |
| // writeable unless its state is set back to Started. The writer might still |
| // transition to the Finished state at any moment, and is allowed to send |
| // didFinishWithError: to its writeable. |
| // |
| // Not all implementations of writer have to support pausing, and thus |
| // trying to set an writer's state to this value might have no effect. |
| GRXWriterStatePaused, |
| |
| // The writer has released its writeable and won't interact with it anymore. |
| // |
| // One seldomly wants to set an writer's state to this value, as its |
| // writeable isn't notified with a didFinishWithError: message. Instead, sending |
| // finishWithError: to the writer will make it notify the writeable and then |
| // transition to this state. |
| GRXWriterStateFinished |
| }; |
| |
| // An object that conforms to this protocol can produce, on demand, a sequence |
| // of values. The sequence may be produced asynchronously, and it may consist of |
| // any number of elements, including none or an infinite number. |
| // |
| // GRXWriter is the active dual of NSEnumerator. The difference between them |
| // is thus whether the object plays an active or passive role during usage: A |
| // user of NSEnumerator pulls values off it, and passes the values to a writeable. |
| // A user of GRXWriter, though, just gives it a writeable, and the |
| // GRXWriter instance pushes values to the writeable. This makes this protocol |
| // suitable to represent a sequence of future values, as well as collections |
| // with internal iteration. |
| // |
| // An instance of GRXWriter can start producing values after a writeable is |
| // passed to it. It can also be commanded to finish the sequence immediately |
| // (with an optional error). Finally, it can be asked to pause, but the |
| // conforming instance is not required to oblige. |
| // |
| // Unless otherwise indicated by a conforming class, no messages should be sent |
| // concurrently to a GRXWriter. I.e., conforming classes aren't required to |
| // be thread-safe. |
| @protocol GRXWriter <NSObject> |
| |
| // This property can be used to query the current state of the writer, which |
| // determines how it might currently use its writeable. Some state transitions can |
| // be triggered by setting this property to the corresponding value, and that's |
| // useful for advanced use cases like pausing an writer. For more details, |
| // see the documentation of the enum. |
| @property(nonatomic) GRXWriterState state; |
| |
| // Start sending messages to the writeable. Messages may be sent before the method |
| // returns, or they may be sent later in the future. See GRXWriteable.h for the |
| // different messages a writeable can receive. |
| // |
| // If this writer draws its values from an external source (e.g. from the |
| // filesystem or from a server), calling this method will commonly trigger side |
| // effects (like network connections). |
| // |
| // This method might only be called on writers in the NotStarted state. |
| - (void)startWithWriteable:(id<GRXWriteable>)writeable; |
| |
| // Send didFinishWithError:errorOrNil immediately to the writeable, and don't send |
| // any more messages to it. |
| // |
| // This method might only be called on writers in the Started or Paused |
| // state. |
| // |
| // TODO(jcanizales): Consider adding some guarantee about the immediacy of that |
| // stopping. I know I've relied on it in part of the code that uses this, but |
| // can't remember the details in the presence of concurrency. |
| - (void)finishWithError:(NSError *)errorOrNil; |
| @end |
| |
| // A "proxy" class that simply forwards values, completion, and errors from its |
| // input writer to its writeable. |
| // It is useful as a superclass for pipes that act as a transformation of their |
| // input writer, and for classes that represent objects with input and |
| // output sequences of values, like an RPC. |
| @interface GRXWriter : NSObject<GRXWriter> |
| - (instancetype)initWithWriter:(id<GRXWriter>)writer NS_DESIGNATED_INITIALIZER; |
| @end |