為什么是函數(shù)式
- 數(shù)據(jù)與函數(shù)是松耦合的
- 函數(shù)隱藏了它們的實(shí)現(xiàn)忘分，語(yǔ)言的抽象是函數(shù)缸剪，以及將函數(shù)組合起來(lái)表達(dá)。
- 核心抽象模型是函數(shù)材部，不是數(shù)據(jù)結(jié)構(gòu)
- 核心活動(dòng)是編寫(xiě)新的函數(shù)毫缆。
- 變量缺省是不變的，減少可變性變量的使用乐导，并發(fā)性好
函數(shù)式的實(shí)現(xiàn)
objc語(yǔ)言使用block實(shí)現(xiàn)函數(shù)式編程苦丁，在典型的函數(shù)式編程框架RAC中，把數(shù)據(jù)的生成和數(shù)據(jù)的處理單獨(dú)的放在block中處理物臂，數(shù)據(jù)的生產(chǎn)和消費(fèi)之間是松耦合的旺拉，block是數(shù)據(jù)處理的最小單位。
本文使用的是Objc版本的ReactiveCocoa棵磷，創(chuàng)建一個(gè)Objc的項(xiàng)目蛾狗，使用pod導(dǎo)入：
pod 'ReactiveObjC', '3.0.0'
創(chuàng)建RACSignal以及訂閱這個(gè)RACSignal接收消息
簡(jiǎn)單的代碼如下
RACSignal* signal = [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber> _Nonnull subscriber) {
[subscriber sendNext:@"message"];
return nil;
}];
[signal subscribeNext:^(id _Nullable x) {
NSLog(@"received:%@", x);
}];
// 控制臺(tái)輸出
2017-04-24 17:36:49.364 EffectiveOCDemo[46385:2426010] received:message
RACSignal對(duì)象創(chuàng)建
// RACSignal.m
+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
return [RACDynamicSignal createSignal:didSubscribe];
}
// RACDynamicSignal.m
+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
RACDynamicSignal *signal = [[self alloc] init];
signal->_didSubscribe = [didSubscribe copy];
return [signal setNameWithFormat:@"+createSignal:"];
}
使用RACSignal類的類方法createSignal創(chuàng)建一個(gè)RACSignal最終創(chuàng)建的是一個(gè)RACSignal的子類RACDynamicSignal的對(duì)象，對(duì)象中會(huì)把參數(shù)中的didSubscribe block 保存到_didSubscribe實(shí)例變量中仪媒，后面發(fā)送消息的時(shí)候回用到_didSubscribe這個(gè)block沉桌。
subscribeNext 方法
// RACSignal.m
- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
NSCParameterAssert(nextBlock != NULL);
RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
return [self subscribe:o];
}
// RACSubscriber.m 快捷方法創(chuàng)建RACSubscriber對(duì)象
+ (instancetype)subscriberWithNext:(void (^)(id x))next error:(void (^)(NSError *error))error completed:(void (^)(void))completed {
RACSubscriber *subscriber = [[self alloc] init];
subscriber->_next = [next copy];
subscriber->_error = [error copy];
subscriber->_completed = [completed copy];
return subscriber;
}
// RACDynamicSignal.m
- (RACDisposable *)subscribe:(id<RACSubscriber>)subscriber {
NSCParameterAssert(subscriber != nil);
RACCompoundDisposable *disposable = [RACCompoundDisposable compoundDisposable];
subscriber = [[RACPassthroughSubscriber alloc] initWithSubscriber:subscriber signal:self disposable:disposable];
if (self.didSubscribe != NULL) {
RACDisposable *schedulingDisposable = [RACScheduler.subscriptionScheduler schedule:^{
RACDisposable *innerDisposable = self.didSubscribe(subscriber);
[disposable addDisposable:innerDisposable];
}];
[disposable addDisposable:schedulingDisposable];
}
return disposable;
}
RACSignal的subscribeNext方法中會(huì)創(chuàng)建了一個(gè)sub，_next成員變量用于保存參數(shù)中的nextBlock，后面接收消息的時(shí)候會(huì)用到_next block留凭。創(chuàng)建了RACSubscriber對(duì)象之后佃扼，調(diào)用RACDynamicSignal對(duì)象的的subscribe方法，并且把RACSubscriber對(duì)象當(dāng)做參數(shù)進(jìn)行傳遞蔼夜。然后執(zhí)行之前保存的didSubscribe block
self.didSubscribe(subscriber);
也就是執(zhí)行了下面這個(gè)block,在這個(gè)block中又會(huì)執(zhí)行RACSubscriber的sendNext方法
RACSignal* signal = [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber> _Nonnull subscriber) {
[subscriber sendNext:@"message"];
return nil;
}];
sendNext方法
- (void)sendNext:(id)value {
@synchronized (self) {
void (^nextBlock)(id) = [self.next copy];
if (nextBlock == nil) return;
nextBlock(value);
}
}
sendNext方法會(huì)同步取出之前保存的next block兼耀，然后執(zhí)行該block,并且傳遞sendNext方法中的參數(shù)，執(zhí)行nextblock也就是執(zhí)行了下面這個(gè)block
[signal subscribeNext:^(id _Nullable x) {
NSLog(@"received:%@", x);
}];
這樣一個(gè)完整的消息發(fā)送接收鏈就創(chuàng)建起來(lái)了求冷，在RACSignal createSignal block中發(fā)送的數(shù)據(jù)在signal subscribeNext block中可以同步的接收到瘤运。
小結(jié)
冷信號(hào)和熱信號(hào)
RACSignal* signal = [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber> _Nonnull subscriber) {
[subscriber sendNext:@"message"];
return nil;
}];
創(chuàng)建的RACSignal對(duì)象里面的didSubscribe并不會(huì)自動(dòng)執(zhí)行，這種RACSignal成為冷信號(hào)遵倦，當(dāng)且僅當(dāng)調(diào)用了subscribeNext訂閱這個(gè)信號(hào)尽超，RACSignal對(duì)象 的didSubscribe才會(huì)得到執(zhí)行官撼，這樣RACSignal成為了熱信號(hào)梧躺，在_didSubscribe block執(zhí)行的時(shí)候同時(shí)會(huì)調(diào)用RACSubscriber sendNext方法，sendNext又會(huì)調(diào)用RACSubscriber的nextBlock傲绣，這樣消息轉(zhuǎn)發(fā)完畢掠哥。
RACSignal數(shù)據(jù)流圖
