@interface RACSignal<__covariant ValueType> : RACStream
/// Creates a new signal. This is the preferred way to create a new signal operation or behavior.
//创建一个新的信号.这是创建新的信号操作或行为的首选方法。
///
/// Events can be sent to new subscribers immediately in the `didSubscribe` block, but the subscriber will not be able to dispose of the signal until a RACDisposable is returned from `didSubscribe`. In the case of infinite signals, this won't _ever_ happen if events are sent immediately.
事件能够在 `didSubscribe` block，立即被订阅者接收，但是，订阅者将无法处理该信号，直到从“didSubscribe”返回一个可使用的数据。在无限信号的情况下，事件将不会被立即发送
（
RACDisposable:用于取消订阅或者清理资源，当信号发送完成或者发送错误的时候，就会自动触发它。
使用场景:不想监听某个信号时，可以通过它主动取消订阅信号。
）
///
/// To ensure that the signal is disposable, events can be scheduled on the +[RACScheduler currentScheduler] (so that they're deferred, not sent immediately), or they can be sent in the background. The RACDisposable returned by the `didSubscribe` block should cancel any such scheduling or asynchronous work.
为了确保信号是一次性的，事件可以通过[RACScheduler currentScheduler]调度（所以它们被推迟了，而不是立即发送。）。或者可以被后台线程处理。The RACDisposable returned by the `didSubscribe` block（取消任何此类调度或异步工作。
RACScheduler ：调度器
有了信号源和订阅者，我们还需要由调度器来统一调度订阅者订阅信号源的过程中所涉及到的任务，这样才能保证所有的任务都能够合理有序地执行。
RACScheduler 在 ReactiveCocoa 中就是扮演着调度器的角色
///
/// didSubscribe - Called when the signal is subscribed to. The new subscriber is passed in. You can then manually control the <RACSubscriber> by sending it -sendNext:, -sendError:, and -sendCompleted, as defined by the operation you're implementing.
didSubscribe -当信号被订阅时调用。新的订阅者被传入，然后，您可以通过发送-sendNext: -sendError:和- sendcomplete来手动控制<RACSubscriber>由您正在实现的操作定义。
This block should return a RACDisposable which cancels any ongoing work triggered by the subscription, and cleans up any resources or disposables created as part of it.
这个“-block”应该返回一个可丢弃的程序，它将取消订阅所触发的任何正在进行的工作，并清理作为它一部分创建的任何资源或可配置文件。
When the disposable is disposed of, the signal must not send any more events to the `subscriber`. If no cleanup is necessary, return nil.
当一次性处理完毕后，信号不能再向“订阅者”发送任何事件。如果不需要清除，则返回nil。
///
/// **Note:** The `didSubscribe` block is called every time a new subscriber subscribes. Any side effects within the block will thus execute once for each subscription, not necessarily on one thread, and possibly even simultaneously!
///注意
“-didSubscribe -block”在每次新的订阅者订阅时都被调用。block内部会被每一个订阅者调用，不一定在一个线程上，甚至可能同时执行
创建信号 + (RACSignal<ValueType> *)createSignal:(RACDisposable * _Nullable (^)(id<RACSubscriber> subscriber))didSubscribe RAC_WARN_UNUSED_RESULT;
/// Returns a signal that immediately sends the given error.
+ (RACSignal<ValueType> *)error:(nullable NSError *)error RAC_WARN_UNUSED_RESULT;
/// Returns a signal that never completes.
+ (RACSignal<ValueType> *)never RAC_WARN_UNUSED_RESULT;
/// Immediately schedules the given block on the given scheduler. The block is given a subscriber to which it can send events.
立即将给定的b_lock安排在给定的调度器上。订阅者可以用这个Block处理事件
///
/// scheduler - The scheduler on which `block` will be scheduled and results delivered. Cannot be nil.
将调度“block”的调度程序和结果。不能为空
/// block - The block to invoke. Cannot be NULL.
///
/// Returns a signal which will send all events sent on the subscriber given to
/// `block`. All events will be sent on `scheduler` and it will replay any missed
/// events to new subscribers.
+ (RACSignal<ValueType> *)startEagerlyWithScheduler:(RACScheduler *)scheduler block:(void (^)(id<RACSubscriber> subscriber))block;
/// Invokes the given block only on the first subscription. The block is given a
/// subscriber to which it can send events.
///
/// Note that disposing of the subscription to the returned signal will *not*
/// dispose of the underlying subscription. If you need that behavior, see
/// -[RACMulticastConnection autoconnect]. The underlying subscription will never
/// be disposed of. Because of this, `block` should never return an infinite
/// signal since there would be no way of ending it.
///
/// scheduler - The scheduler on which the block should be scheduled. Note that
/// if given +[RACScheduler immediateScheduler], the block will be
/// invoked synchronously on the first subscription. Cannot be nil.
/// block - The block to invoke on the first subscription. Cannot be NULL.
///
/// Returns a signal which will pass through the events sent to the subscriber
/// given to `block` and replay any missed events to new subscribers.
+ (RACSignal<ValueType> *)startLazilyWithScheduler:(RACScheduler *)scheduler block:(void (^)(id<RACSubscriber> subscriber))block RAC_WARN_UNUSED_RESULT;
@end
@interface RACSignal<__covariant ValueType> (RACStream)
/// Returns a signal that immediately sends the given value and then completes.
返回一个信号，该信号立即发送给定的值，然后完成。
+ (RACSignal<ValueType> *)return:(nullable ValueType)value RAC_WARN_UNUSED_RESULT;
/// Returns a signal that immediately completes.
返回立即完成的信号。
+ (RACSignal<ValueType> *)empty RAC_WARN_UNUSED_RESULT;
/// A block which accepts a value from a RACSignal and returns a new signal.
///
/// Setting `stop` to `YES` will cause the bind to terminate after the returned
/// value. Returning `nil` will result in immediate termination.
typedef RACSignal * _Nullable (^RACSignalBindBlock)(ValueType _Nullable value, BOOL *stop);
/// Lazily binds a block to the values in the receiver.
///
/// This should only be used if you need to terminate the bind early, or close
/// over some state. -flattenMap: is more appropriate for all other cases.
///
/// block - A block returning a RACSignalBindBlock. This block will be invoked
/// each time the bound signal is re-evaluated. This block must not be
/// nil or return nil.
///
/// Returns a new signal which represents the combined result of all lazy
/// applications of `block`.
///返回一个新信号，该信号表示“b_lock”的所有惰性应用程序的组合结果。
- (RACSignal *)bind:(RACSignalBindBlock (^)(void))block RAC_WARN_UNUSED_RESULT;
/// Subscribes to `signal` when the source signal completes.
当源信号完成时，订阅“信号”。
- (RACSignal *)concat:(RACSignal *)signal RAC_WARN_UNUSED_RESULT;
/// Zips the values in the receiver with those of the given signal to create
/// RACTuples.
///
/// The first `next` of each signal will be combined, then the second `next`,
/// and so forth, until either signal completes or errors.
///
/// signal - The signal to zip with. This must not be `nil`.
///
/// Returns a new signal of RACTuples, representing the combined values of the
/// two signals. Any error from one of the original signals will be forwarded on
/// the returned signal.
- (RACSignal<RACTwoTuple<ValueType, id> *> *)zipWith:(RACSignal *)signal RAC_WARN_UNUSED_RESULT;
@end
/// Redeclarations of operations built on the RACStream primitives with more
/// precise ValueType information.
///
/// In cases where the ValueType of the result of the operation is not able to
/// be inferred, the ValueType is erased in the result.
///
/// In cases where instancetype is a valid return type, the operation is not
/// redeclared here.
@interface RACSignal<__covariant ValueType> (RACStreamOperations)
/// Maps `block` across the values in the receiver and flattens the result.
///
/// Note that operators applied _after_ -flattenMap: behave differently from
/// operators _within_ -flattenMap:. See the Examples section below.
///
/// This corresponds to the `SelectMany` method in Rx.
///
/// block - A block which accepts the values in the receiver and returns a new
/// instance of the receiver's class. Returning `nil` from this block is
/// equivalent to returning an empty signal.
///
/// Examples
///
/// [signal flattenMap:^(id x) {
/// // Logs each time a returned signal completes.
/// return [[RACSignal return:x] logCompleted];
/// }];
///
/// [[signal
/// flattenMap:^(id x) {
/// return [RACSignal return:x];
/// }]
/// // Logs only once, when all of the signals complete.
/// logCompleted];
///
/// Returns a new signal which represents the combined signals resulting from
/// mapping `block`.
- (RACSignal *)flattenMap:(__kindof RACSignal * _Nullable (^)(ValueType _Nullable value))block RAC_WARN_UNUSED_RESULT;
/// Flattens a signal of signals.
///
/// This corresponds to the `Merge` method in Rx.
///
/// Returns a signal consisting of the combined signals obtained from the
/// receiver.
- (RACSignal *)flatten RAC_WARN_UNUSED_RESULT;
/// Maps `block` across the values in the receiver.
///
/// This corresponds to the `Select` method in Rx.
///
/// Returns a new signal with the mapped values.
- (RACSignal *)map:(id _Nullable (^)(ValueType _Nullable value))block RAC_WARN_UNUSED_RESULT;
/// Replaces each value in the receiver with the given object.
///
/// Returns a new signal which includes the given object once for each value in
/// the receiver.
- (RACSignal *)mapReplace:(nullable id)object RAC_WARN_UNUSED_RESULT;
/// Filters out values in the receiver that don't pass the given test.
///
/// This corresponds to the `Where` method in Rx.
///
/// Returns a new signal with only those values that passed.
- (RACSignal<ValueType> *)filter:(BOOL (^)(ValueType _Nullable value))block RAC_WARN_UNUSED_RESULT;
/// Filters out values in the receiver that equal (via -isEqual:) the provided
/// value.
///
/// value - The value can be `nil`, in which case it ignores `nil` values.
///
/// Returns a new signal containing only the values which did not compare equal
/// to `value`.
- (RACSignal<ValueType> *)ignore:(nullable ValueType)value RAC_WARN_UNUSED_RESULT;
/// Unpacks each RACTuple in the receiver and maps the values to a new value.
///
/// reduceBlock - The block which reduces each RACTuple's values into one value.
/// It must take as many arguments as the number of tuple elements
/// to process. Each argument will be an object argument. The
/// return value must be an object. This argument cannot be nil.
///
/// Returns a new signal of reduced tuple values.
- (RACSignal *)reduceEach:(id _Nullable (^)())reduceBlock RAC_WARN_UNUSED_RESULT;
/// Returns a signal consisting of `value`, followed by the values in the
/// receiver.
- (RACSignal<ValueType> *)startWith:(nullable ValueType)value RAC_WARN_UNUSED_RESULT;
/// Skips the first `skipCount` values in the receiver.
///
/// Returns the receiver after skipping the first `skipCount` values. If
/// `skipCount` is greater than the number of values in the signal, an empty
/// signal is returned.
- (RACSignal<ValueType> *)skip:(NSUInteger)skipCount RAC_WARN_UNUSED_RESULT;
/// Returns a signal of the first `count` values in the receiver. If `count` is
/// greater than or equal to the number of values in the signal, a signal
/// equivalent to the receiver is returned.
- (RACSignal<ValueType> *)take:(NSUInteger)count RAC_WARN_UNUSED_RESULT;
/// Zips the values in the given signals to create RACTuples.
///
/// The first value of each signals will be combined, then the second value, and
/// so forth, until at least one of the signals is exhausted.
///
/// signals - The signals to combine. If this collection is empty, the returned
/// signal will be empty.
///
/// Returns a new signal containing RACTuples of the zipped values from the
/// signals.
+ (RACSignal<RACTuple *> *)zip:(id<NSFastEnumeration>)signals RAC_WARN_UNUSED_RESULT;
/// Zips signals using +zip:, then reduces the resulting tuples into a single
/// value using -reduceEach:
///
/// signals - The signals to combine. If this collection is empty, the
/// returned signal will be empty.
/// reduceBlock - The block which reduces the values from all the signals
/// into one value. It must take as many arguments as the
/// number of signals given. Each argument will be an object
/// argument. The return value must be an object. This argument
/// must not be nil.
///
/// Example:
///
/// [RACSignal zip:@[ stringSignal, intSignal ]
/// reduce:^(NSString *string, NSNumber *number) {
/// return [NSString stringWithFormat:@"%@: %@", string, number];
/// }];
///
/// Returns a new signal containing the results from each invocation of
/// `reduceBlock`.
+ (RACSignal<ValueType> *)zip:(id<NSFastEnumeration>)signals reduce:(id _Nullable (^)())reduceBlock RAC_WARN_UNUSED_RESULT;
/// Returns a signal obtained by concatenating `signals` in order.
+ (RACSignal<ValueType> *)concat:(id<NSFastEnumeration>)signals RAC_WARN_UNUSED_RESULT;
/// Combines values in the receiver from left to right using the given block.
///
/// The algorithm proceeds as follows:
///
/// 1. `startingValue` is passed into the block as the `running` value, and the
/// first element of the receiver is passed into the block as the `next` value.
/// 2. The result of the invocation is added to the returned signal.
/// 3. The result of the invocation (`running`) and the next element of the
/// receiver (`next`) is passed into `block`.
/// 4. Steps 2 and 3 are repeated until all values have been processed.
///
/// startingValue - The value to be combined with the first element of the
/// receiver. This value may be `nil`.
/// reduceBlock - The block that describes how to combine values of the
/// receiver. If the receiver is empty, this block will never be
/// invoked. Cannot be nil.
///
/// Examples
///
/// RACSequence *numbers = @[ @1, @2, @3, @4 ].rac_sequence;
///
/// // Contains 1, 3, 6, 10
/// RACSequence *sums = [numbers scanWithStart:@0 reduce:^(NSNumber *sum, NSNumber *next) {
/// return @(sum.integerValue + next.integerValue);
/// }];
///
/// Returns a new signal that consists of each application of `reduceBlock`. If
/// the receiver is empty, an empty signal is returned.
- (RACSignal *)scanWithStart:(nullable id)startingValue reduce:(id _Nullable (^)(id _Nullable running, ValueType _Nullable next))reduceBlock RAC_WARN_UNUSED_RESULT;
/// Combines values in the receiver from left to right using the given block
/// which also takes zero-based index of the values.
///
/// startingValue - The value to be combined with the first element of the
/// receiver. This value may be `nil`.
/// reduceBlock - The block that describes how to combine values of the
/// receiver. This block takes zero-based index value as the last
/// parameter. If the receiver is empty, this block will never
/// be invoked. Cannot be nil.
///
/// Returns a new signal that consists of each application of `reduceBlock`. If
/// the receiver is empty, an empty signal is returned.
- (RACSignal *)scanWithStart:(nullable id)startingValue reduceWithIndex:(id _Nullable (^)(id _Nullable running, ValueType _Nullable next, NSUInteger index))reduceBlock RAC_WARN_UNUSED_RESULT;
/// Combines each previous and current value into one object.
///
/// This method is similar to -scanWithStart:reduce:, but only ever operates on
/// the previous and current values (instead of the whole signal), and does not
/// pass the return value of `reduceBlock` into the next invocation of it.
///
/// start - The value passed into `reduceBlock` as `previous` for the
/// first value.
/// reduceBlock - The block that combines the previous value and the current
/// value to create the reduced value. Cannot be nil.
///
/// Examples
///
/// RACSignal<NSNumber *> *numbers = [@[ @1, @2, @3, @4 ].rac_sequence
/// signalWithScheduler:RACScheduler.immediateScheduler];
///
/// // Contains 1, 3, 5, 7
/// RACSignal *sums = [numbers combinePreviousWithStart:@0 reduce:^(NSNumber *previous, NSNumber *next) {
/// return @(previous.integerValue + next.integerValue);
/// }];
///
/// Returns a new signal consisting of the return values from each application of
/// `reduceBlock`.
- (RACSignal *)combinePreviousWithStart:(nullable ValueType)start reduce:(id _Nullable (^)(ValueType _Nullable previous, ValueType _Nullable current))reduceBlock RAC_WARN_UNUSED_RESULT;
/// Takes values until the given block returns `YES`.
///
/// Returns a signal of the initial values in the receiver that fail `predicate`.
/// If `predicate` never returns `YES`, a signal equivalent to the receiver is
/// returned.
- (RACSignal<ValueType> *)takeUntilBlock:(BOOL (^)(ValueType _Nullable x))predicate RAC_WARN_UNUSED_RESULT;
/// Takes values until the given block returns `NO`.
///
/// Returns a signal of the initial values in the receiver that pass `predicate`.
/// If `predicate` never returns `NO`, a signal equivalent to the receiver is
/// returned.
- (RACSignal<ValueType> *)takeWhileBlock:(BOOL (^)(ValueType _Nullable x))predicate RAC_WARN_UNUSED_RESULT;
/// Skips values until the given block returns `YES`.
///
/// Returns a signal containing the values of the receiver that follow any
/// initial values failing `predicate`. If `predicate` never returns `YES`,
/// an empty signal is returned.
- (RACSignal<ValueType> *)skipUntilBlock:(BOOL (^)(ValueType _Nullable x))predicate RAC_WARN_UNUSED_RESULT;
/// Skips values until the given block returns `NO`.
///
/// Returns a signal containing the values of the receiver that follow any
/// initial values passing `predicate`. If `predicate` never returns `NO`, an
/// empty signal is returned.
- (RACSignal<ValueType> *)skipWhileBlock:(BOOL (^)(ValueType _Nullable x))predicate RAC_WARN_UNUSED_RESULT;
/// Returns a signal of values for which -isEqual: returns NO when compared to the
/// previous value.
- (RACSignal<ValueType> *)distinctUntilChanged RAC_WARN_UNUSED_RESULT;
@end
@interface RACSignal<__covariant ValueType> (Subscription)
/// Subscribes `subscriber` to changes on the receiver. The receiver defines which
/// events it actually sends and in what situations the events are sent.
///
/// Subscription will always happen on a valid RACScheduler. If the
/// +[RACScheduler currentScheduler] cannot be determined at the time of
/// subscription (e.g., because the calling code is running on a GCD queue or
/// NSOperationQueue), subscription will occur on a private background scheduler.
/// On the main thread, subscriptions will always occur immediately, with a
/// +[RACScheduler currentScheduler] of +[RACScheduler mainThreadScheduler].
///
/// This method must be overridden by any subclasses.
这个方法必须被任何子类覆盖。
///
/// Returns nil or a disposable. You can call -[RACDisposable dispose] if you
/// need to end your subscription before it would "naturally" end, either by
/// completing or erroring. Once the disposable has been disposed, the subscriber
/// won't receive any more events from the subscription.
You can call -[RACDisposable dispose]如果你需要结束你的订阅，它将“自然”结束，或者是完成或错误。一旦处理完毕，订阅者将不再接收来自订阅的任何事件。
- (RACDisposable *)subscribe:(id<RACSubscriber>)subscriber;
/// Convenience method to subscribe to the `next` event.
///
/// This corresponds to `IObserver<T>.OnNext` in Rx.
- (RACDisposable *)subscribeNext:(void (^)(ValueType _Nullable x))nextBlock;
/// Convenience method to subscribe to the `next` and `completed` events.
- (RACDisposable *)subscribeNext:(void (^)(ValueType _Nullable x))nextBlock completed:(void (^)(void))completedBlock;
/// Convenience method to subscribe to the `next`, `completed`, and `error` events.
- (RACDisposable *)subscribeNext:(void (^)(ValueType _Nullable x))nextBlock error:(void (^)(NSError * _Nullable error))errorBlock completed:(void (^)(void))completedBlock;
/// Convenience method to subscribe to `error` events.
///
/// This corresponds to the `IObserver<T>.OnError` in Rx.
- (RACDisposable *)subscribeError:(void (^)(NSError * _Nullable error))errorBlock;
/// Convenience method to subscribe to `completed` events.
订阅“已完成”事件的便利方法。
///
/// This corresponds to the `IObserver<T>.OnCompleted` in Rx.
- (RACDisposable *)subscribeCompleted:(void (^)(void))completedBlock;
/// Convenience method to subscribe to `next` and `error` events.
订阅“next”和“error”事件的便利方法。
- (RACDisposable *)subscribeNext:(void (^)(ValueType _Nullable x))nextBlock error:(void (^)(NSError * _Nullable error))errorBlock;
/// Convenience method to subscribe to `error` and `completed` events.
订阅“错误”和“完成”事件的便利方法。
- (RACDisposable *)subscribeError:(void (^)(NSError * _Nullable error))errorBlock completed:(void (^)(void))completedBlock;
@end
/// Additional methods to assist with debugging.
辅助调试的其他方法。
@interface RACSignal<__covariant ValueType> (Debugging)
/// Logs all events that the receiver sends.
- (RACSignal<ValueType> *)logAll RAC_WARN_UNUSED_RESULT;
/// Logs each `next` that the receiver sends.
记录接收方发送的所有事件。
- (RACSignal<ValueType> *)logNext RAC_WARN_UNUSED_RESULT;
/// Logs any error that the receiver sends.
- (RACSignal<ValueType> *)logError RAC_WARN_UNUSED_RESULT;
/// Logs any `completed` event that the receiver sends.
- (RACSignal<ValueType> *)logCompleted RAC_WARN_UNUSED_RESULT;
@end
/// Additional methods to assist with unit testing.
辅助单元测试的其他方法。
///
/// **These methods should never ship in production code.**
这些方法不应该在生产环境代码中使用。
@interface RACSignal<__covariant ValueType> (Testing)
/// Spins the main run loop for a short while, waiting for the receiver to send a `next`.
///
/// **Because this method executes the run loop recursively, it should only be used
/// on the main thread, and only from a unit test.**
///
/// defaultValue - Returned if the receiver completes or errors before sending
/// a `next`, or if the method times out. This argument may be
/// nil.
/// success - If not NULL, set to whether the receiver completed
/// successfully.
/// error - If not NULL, set to any error that occurred.
///
/// Returns the first value received, or `defaultValue` if no value is received
/// before the signal finishes or the method times out.
- (nullable ValueType)asynchronousFirstOrDefault:(nullable ValueType)defaultValue success:(nullable BOOL *)success error:(NSError * _Nullable * _Nullable)error;
/// Spins the main run loop for a short while, waiting for the receiver to complete.
///
/// **Because this method executes the run loop recursively, it should only be used
/// on the main thread, and only from a unit test.**
由于该方法递归地执行运行循环，所以它只能在主线程上使用，而且只能在单元测试中使用。
///
/// error - If not NULL, set to any error that occurs.
///
/// Returns whether the signal completed successfully before timing out. If NO,
/// `error` will be set to any error that occurred.
返回是否在超时前成功完成信号。
- (BOOL)asynchronouslyWaitUntilCompleted:(NSError * _Nullable * _Nullable)error;
@end