1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
|
/*
*
* 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"
// 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 a writer
// transition to the Started state, send it a startWithWriteable: message.
//
// 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.
GRXWriterStatePaused,
// The writer has released its writeable and won't interact with it anymore.
//
// 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 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.
//
// 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.
//
// Thread-safety:
//
// 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 further down.
@property(nonatomic) GRXWriterState state;
// 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).
//
// This method might only be called on writers in the NotStarted state.
- (void)startWithWriteable:(id<GRXWriteable>)writeable;
// Send writesFinishedWithError:errorOrNil to the writeable. Then release the reference to it and
// transition to the Finished state.
//
// This method might only be called on writers in the Started or Paused state.
- (void)finishWithError:(NSError *)errorOrNil;
@end
|
