图解ReactiveCocoa基本函数

本文讨论仅限于ReactiveCocoa v2.5

关于函数响应式编程（FRP），可以参考

What is (functional) reactive programming?

Specification for a Functional Reactive Programming language



Streams of values over time

ReactiveCocoa repo上最简单的一句话对FRP做了本质的描述，而repo本身提供的是APIs of composing and transforming streams of values，而Streams of values的抽象在ReactiveCocoa中应该是RACStream，而要composing and transforming是本文想要描述的核心内容。

先解释ReactiveCocoa中的两个基本概念

信号（Signal） a signal is a steam of values，signals can be transformed, combined,etc.

订阅者（Subscriber） a subscriber subscribes to a signal. RAC lets blocks,objects, and properties subscribe to signals

filter

RACSignal *signal = [@[ @1, @2, @3 ] rac_sequence].signal; signal = [signal filter:^BOOL(NSNumber *value) {
return value.integerValue % 2;
}];
[signal subscribeNext:^(NSNumber *value) {
NSLog(@"%@", value);
}];

map

RACSignal *signal1 = [@[ @1, @2 ] rac_sequence].signal;
RACSignal *signal2 = [@[ @4, @5 ] rac_sequence].signal;

[[signal1 merge:signal2] subscribeNext:^(NSNumber *value) {
NSLog(@"%@", value);
}];

merge

RACSignal *signal1 = [@[ @1, @2 ] rac_sequence].signal;
RACSignal *signal2 = [@[ @4, @5 ] rac_sequence].signal;

[[signal1 merge:signal2] subscribeNext:^(NSNumber *value) {
NSLog(@"%@", value);
}];

combineLatest

RACSignal *signal1 = [@[ @1, @2 ] rac_sequence].signal;
RACSignal *signal2 = [@[ @3, @4 ] rac_sequence].signal;

[[signal1 combineLatestWith:signal2] subscribeNext:^(NSNumber *value) {
NSLog(@"%@", value);
}];

combineLatest & reduce

RACSignal *signal1 = [@[ @1, @2 ] rac_sequence].signal;
RACSignal *signal2 = [@[ @3, @4 ] rac_sequence].signal;

[[[signal1 combineLatestWith:signal2]
reduceEach:^id(NSNumber *v1, NSNumber *v2) {
return @(v1.integerValue * v2.integerValue);
}] subscribeNext:^(NSNumber *value) {
NSLog(@"%@", value);
}];

flatten

RACSignal *signal1 = [@[ @1, @2 ] rac_sequence].signal;
RACSignal *signal2 = [RACSignal return:signal1];

[[signal2 flatten] subscribeNext:^(NSNumber *value) {
NSLog(@"%@", value);
}];

flattenMap

RACSignal *signal = [@[ @1, @2 ] rac_sequence].signal;

[[signal flattenMap:^RACStream *(NSNumber *value) {
return [RACSignal return:@(value.integerValue * 2)];
}] subscribeNext:^(NSNumber *value) {
NSLog(@"%@", value);
}];

not replay

RACSubject *letters = [RACSubject subject];
RACSignal *signal = letters;
[signal subscribeNext:^(id x) {
NSLog(@"S1: %@", x);
}];
[letters sendNext:@"A"];
[letters sendNext:@"B"];
[signal subscribeNext:^(id x) {
NSLog(@"S2: %@", x);
}];
[letters sendNext:@"C"];

replay

RACSubject *letters = [RACReplaySubject subject];
RACSignal *signal = letters;
[signal subscribeNext:^(id x) {
NSLog(@"S1: %@", x);
}];
[letters sendNext:@"A"];
[signal subscribeNext:^(id x) {
NSLog(@"S2: %@", x);
}];
[letters sendNext:@"B"];
[signal subscribeNext:^(id x) {
NSLog(@"S3: %@", x);
}];
[letters sendNext:@"C"];

replayLast

RACSubject *letters = [RACSubject subject];
RACSignal *signal = [letters replayLast];
[signal subscribeNext:^(id x) {
NSLog(@"S1: %@", x);
}];
[letters sendNext:@"A"];
[signal subscribeNext:^(id x) {
NSLog(@"S2: %@", x);
}];
[letters sendNext:@"B"];
[signal subscribeNext:^(id x) {
NSLog(@"S3: %@", x);
}];
[letters sendNext:@"C"];

replayLazily

RACSubject *letters = [RACSubject subject];
RACSignal *signal = [letters replayLazily];
[letters sendNext:@"A"];
[signal subscribeNext:^(id x) {
NSLog(@"S1: %@", x);
}];
[letters sendNext:@"B"];
[signal subscribeNext:^(id x) {
NSLog(@"S2: %@", x);
}];
[letters sendNext:@"C"];
[signal subscribeNext:^(id x) {
NSLog(@"S3: %@", x);
}];
[letters sendNext:@"D"];

zip

RACSubject *letters = [RACSubject subject];
RACSubject *numbers = [RACSubject subject];

RACSignal *combined =
[RACSignal zip:@[ letters, numbers ]
reduce:^(NSString *letter, NSString *number) {
return [letter stringByAppendingString:number];
}];

// Outputs: A1 B2 C3
[combined subscribeNext:^(id x) {
NSLog(@"%@", x);
}];

[letters sendNext:@"A"];
[letters sendNext:@"B"];
[letters sendNext:@"C"];
[numbers sendNext:@"1"];
[numbers sendNext:@"2"];
[numbers sendNext:@"3"];