diff options
Diffstat (limited to 'src/objective-c/RxLibrary/GRXWriter.h')
| -rw-r--r-- | src/objective-c/RxLibrary/GRXWriter.h | 91 |
1 files changed, 40 insertions, 51 deletions
diff --git a/src/objective-c/RxLibrary/GRXWriter.h b/src/objective-c/RxLibrary/GRXWriter.h index 5d6e1a472a..b1c994aa38 100644 --- a/src/objective-c/RxLibrary/GRXWriter.h +++ b/src/objective-c/RxLibrary/GRXWriter.h @@ -35,84 +35,73 @@ #import "GRXWriteable.h" +// States of a writer. 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. + // The writer has not yet been given a writeable to which it can push its values. To have a writer + // transition to the Started state, send it a startWithWriteable: message. // - // An writer's state cannot be manually set to this value. + // A 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 - // writesFinishedWithError: 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. + // 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 writesFinishedWithError: to its writeable. 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 writesFinishedWithError: message. Instead, sending - // finishWithError: to the writer will make it notify the writeable and then - // transition to this state. + // One seldomly wants to set a writer's state to this value, as its writeable isn't notified with + // a writesFinishedWithError: 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. +// An GRXWriter object 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. // -// 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, and resumed later. All GRXWriter objects support pausing and early termination. // -// 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. +// Thread-safety: // -// 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. +// State transitions take immediate effect if the object is used from a single thread. Subclasses +// might offer stronger guarantees. +// +// Unless otherwise indicated by a conforming subclass, no messages should be sent concurrently to a +// GRXWriter. I.e., conforming classes aren't required to be thread-safe. @interface 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. +// 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 further down. @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. +// Transition to the Started state, and start sending messages to the writeable (a reference to it +// is retained). Messages to the writeable 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). +// 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 writesFinishedWithError: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. +// Send writesFinishedWithError:errorOrNil to the writeable. Then release the reference to it and +// transition to the Finished 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. +// This method might only be called on writers in the Started or Paused state. - (void)finishWithError:(NSError *)errorOrNil; @end |