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@ -35,73 +35,87 @@ |
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#import "GRXWriteable.h" |
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// States of a writer.
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/** States of a writer. */ |
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typedef NS_ENUM(NSInteger, GRXWriterState) { |
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// The writer has not yet been given a writeable to which it can push its values. To have a writer
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// transition to the Started state, send it a startWithWriteable: message.
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//
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// A writer's state cannot be manually set to this value.
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/**
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* The writer has not yet been given a writeable to which it can push its values. To have a writer |
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* transition to the Started state, send it a startWithWriteable: message. |
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* |
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* A writer's state cannot be manually set to this value. |
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*/ |
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GRXWriterStateNotStarted, |
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// The writer might push values to the writeable at any moment.
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/** The writer might push values to the writeable at any moment. */ |
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GRXWriterStateStarted, |
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// The writer is temporarily paused, and won't send any more values to the writeable unless its
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// state is set back to Started. The writer might still transition to the Finished state at any
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// moment, and is allowed to send writesFinishedWithError: to its writeable.
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/**
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* The writer is temporarily paused, and won't send any more values to the writeable unless its |
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* state is set back to Started. The writer might still transition to the Finished state at any |
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* moment, and is allowed to send writesFinishedWithError: to its writeable. |
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*/ |
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GRXWriterStatePaused, |
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// The writer has released its writeable and won't interact with it anymore.
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//
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// One seldomly wants to set a writer's state to this value, as its writeable isn't notified with
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// a writesFinishedWithError: message. Instead, sending finishWithError: to the writer will make
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// it notify the writeable and then transition to this state.
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/**
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* The writer has released its writeable and won't interact with it anymore. |
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* |
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* One seldomly wants to set a writer's state to this value, as its writeable isn't notified with |
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* a writesFinishedWithError: message. Instead, sending finishWithError: to the writer will make |
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* it notify the writeable and then transition to this state. |
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*/ |
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GRXWriterStateFinished |
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}; |
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// An GRXWriter object can produce, on demand, a sequence of values. The sequence may be produced
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// asynchronously, and it may consist of any number of elements, including none or an infinite
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// number.
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//
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// GRXWriter is the active dual of NSEnumerator. The difference between them is thus whether the
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// object plays an active or passive role during usage: A user of NSEnumerator pulls values off it,
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// and passes the values to a writeable. A user of GRXWriter, though, just gives it a writeable, and
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// the GRXWriter instance pushes values to the writeable. This makes this protocol suitable to
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// represent a sequence of future values, as well as collections with internal iteration.
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//
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// An instance of GRXWriter can start producing values after a writeable is passed to it. It can
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// also be commanded to finish the sequence immediately (with an optional error). Finally, it can be
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// asked to pause, and resumed later. All GRXWriter objects support pausing and early termination.
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//
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// Thread-safety:
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//
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// State transitions take immediate effect if the object is used from a single thread. Subclasses
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// might offer stronger guarantees.
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//
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// Unless otherwise indicated by a conforming subclass, no messages should be sent concurrently to a
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// GRXWriter. I.e., conforming classes aren't required to be thread-safe.
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/**
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* An GRXWriter object can produce, on demand, a sequence of values. The sequence may be produced |
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* asynchronously, and it may consist of any number of elements, including none or an infinite |
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* number. |
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* |
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* GRXWriter is the active dual of NSEnumerator. The difference between them is thus whether the |
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* object plays an active or passive role during usage: A user of NSEnumerator pulls values off it, |
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* and passes the values to a writeable. A user of GRXWriter, though, just gives it a writeable, and |
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* the GRXWriter instance pushes values to the writeable. This makes this protocol suitable to |
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* represent a sequence of future values, as well as collections with internal iteration. |
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* |
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* An instance of GRXWriter can start producing values after a writeable is passed to it. It can |
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* also be commanded to finish the sequence immediately (with an optional error). Finally, it can be |
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* asked to pause, and resumed later. All GRXWriter objects support pausing and early termination. |
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* |
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* Thread-safety: |
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* |
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* State transitions take immediate effect if the object is used from a single thread. Subclasses |
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* might offer stronger guarantees. |
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* |
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* Unless otherwise indicated by a conforming subclass, no messages should be sent concurrently to a |
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* GRXWriter. I.e., conforming classes aren't required to be thread-safe. |
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*/ |
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@interface GRXWriter : NSObject |
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// This property can be used to query the current state of the writer, which determines how it might
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// currently use its writeable. Some state transitions can be triggered by setting this property to
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// the corresponding value, and that's useful for advanced use cases like pausing an writer. For
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// more details, see the documentation of the enum further down.
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/**
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* This property can be used to query the current state of the writer, which determines how it might |
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* currently use its writeable. Some state transitions can be triggered by setting this property to |
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* the corresponding value, and that's useful for advanced use cases like pausing an writer. For |
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* more details, see the documentation of the enum further down. |
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*/ |
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@property(nonatomic) GRXWriterState state; |
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// Transition to the Started state, and start sending messages to the writeable (a reference to it
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// is retained). Messages to the writeable may be sent before the method returns, or they may be
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// sent later in the future. See GRXWriteable.h for the different messages a writeable can receive.
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//
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// If this writer draws its values from an external source (e.g. from the filesystem or from a
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// server), calling this method will commonly trigger side effects (like network connections).
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//
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// This method might only be called on writers in the NotStarted state.
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/**
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* Transition to the Started state, and start sending messages to the writeable (a reference to it |
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* is retained). Messages to the writeable may be sent before the method returns, or they may be |
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* sent later in the future. See GRXWriteable.h for the different messages a writeable can receive. |
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* |
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* If this writer draws its values from an external source (e.g. from the filesystem or from a |
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* server), calling this method will commonly trigger side effects (like network connections). |
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* |
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* This method might only be called on writers in the NotStarted state. |
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*/ |
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- (void)startWithWriteable:(id<GRXWriteable>)writeable; |
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// Send writesFinishedWithError:errorOrNil to the writeable. Then release the reference to it and
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// transition to the Finished state.
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//
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// This method might only be called on writers in the Started or Paused state.
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/**
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* Send writesFinishedWithError:errorOrNil to the writeable. Then release the reference to it and |
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* transition to the Finished state. |
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* |
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* This method might only be called on writers in the Started or Paused state. |
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*/ |
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- (void)finishWithError:(NSError *)errorOrNil; |
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@end |
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