However, I had no idea if I could define a generic Interface, let alone implement one. Even assuming I could do both of those things, would Delphi be able to resolve the correct Receive method to invoke? Only one way to find out\u2026.<\/p>\n
NB: In this example, I\u2019ve stripped out most of the pub\/sub stuff, just leaving the pieces needed to show the generic interfaces. I\u2019ll write about the other pieces over the next few posts.<\/p>\n
First, I implemented a few sample events. The contents of these are not that interesting:<\/p>\n
TSomeEvent = class\r\n \/\/ other stuff \r\nend;\r\n\r\nTSomeOtherEvent = class\r\n \/\/ other stuff \r\nend;<\/pre>\nThen, I defined a generic interface<\/p>\n
ISubscriber = interface\r\n procedure Receive(Event : T); \r\nend;<\/pre>\nThis is the interface that will need to be implemented by my subscribers in order to receive events of a particular type. Note, the type of event is set up as a generic type T.<\/p>\n
Then, my subscribers need to implement an interface for each Event type they want to receive, however because it is a generic interface, it\u2019s pretty straight-forward:<\/p>\n
TMySubscribingObject = class(TInterfacedObject, ISubscriber, ISubscriber)\r\nprotected\r\n procedure Receive(Event : TSomeEvent); overload; \r\n procedure Receive(Event : TSomeOtherEvent); overload; \r\nend;<\/pre>\nNote there\u2019s no definition of a ISomeEventSubscriber and a ISomeOtherEventSubscriber interface, we can just use ISubscriber<T> and pass the type in in-place. We just need to implement the necessary overloaded Receive events.<\/p>\n
You can see the rest of the code in the associated test project<\/a>, but the above shows you the main aim. Implementing multiple interfaces, each with a strongly-typed Receive event, without actually having to define each of those interfaces.<\/p>\nSo, does it work? Well, at my first attempt, no, it didn\u2019t. No matter what type of Event I passed in, or via what interface, it always invoked the last Receive method.<\/p>\n
![\"dunit_generic_interfaces\"](\"http:\/\/www.malcolmgroves.com\/blog\/wp-content\/uploads\/2009\/07\/dunit-generic-interfaces-thumb1.jpg\" "\\"dunit_generic_interfaces\\"")
<\/a>Rule of life #37: If it\u2019s a choice between Malcolm having screwed up or the Delphi compiler architects, it\u2019s probably Malcolm\u2019s fault.<\/p>\n