Subclass GRXWriter instead of conforming to protocol
diff --git a/src/objective-c/RxLibrary/GRXImmediateWriter.h b/src/objective-c/RxLibrary/GRXImmediateWriter.h
index 0ba4ac4..b171f0c 100644
--- a/src/objective-c/RxLibrary/GRXImmediateWriter.h
+++ b/src/objective-c/RxLibrary/GRXImmediateWriter.h
@@ -40,7 +40,7 @@
//
// Unless the writeable callback pauses them or stops them early, these writers will do all their
// interactions with the writeable before the start method returns.
-@interface GRXImmediateWriter : NSObject<GRXWriter>
+@interface GRXImmediateWriter : GRXWriter
// Returns a writer that pulls values from the passed NSEnumerator instance and pushes them to
// its writeable. The NSEnumerator is released when it finishes.