added CachedPublisher

broqer/__init__.py

@@ -1,5 +1,7 @@
 # -*- coding: utf-8 -*-
-from .core import Disposable, Publisher, Subscriber, SubscriptionDisposable
+from .core import CachedPublisher, Disposable, Publisher, Subscriber, \
+                  SubscriptionDisposable
+
 from .hub import Hub, SubHub
 from .subject import Subject, Value
 from .default_error_handler import default_error_handler
@@ -9,6 +11,7 @@
 __version__ = '0.3.2-dev'
 
 __all__ = [
-    'Disposable', 'SubscriptionDisposable', 'Subscriber', 'Publisher',
-    'Subject', 'Value', 'Hub', 'SubHub', 'default_error_handler'
+    'CachedPublisher', 'Disposable', 'Publisher', 'Subscriber',
+    'SubscriptionDisposable', 'Hub', 'SubHub', 'Subject', 'Value',
+    'default_error_handler'
 ]

broqer/core.py

@@ -75,6 +75,25 @@ def __await__(self):
         return ToFuture(self).__await__()
 
 
+class CachedPublisher(Publisher):
+    def __init__(self, *init):
+        Publisher.__init__(self)
+        if not init:
+            self._cache = None
+        else:
+            self._cache = init
+
+    def subscribe(self, subscriber: 'Subscriber') -> SubscriptionDisposable:
+        disposable = Publisher.subscribe(self, subscriber)
+        if self._cache is not None:
+            subscriber.emit(*self._cache, who=self)
+        return disposable
+
+    def _emit(self, *args: Any) -> None:
+        self._cache = args
+        Publisher._emit(self, *args)
+
+
 class Subscriber(metaclass=ABCMeta):
     @abstractmethod
     def emit(self, *args: Any, who: Publisher) -> None: