Subscribing to events without unsubscribing later on can lead to memory leaks or even duplicate subscriptions, i.e. code which is executed multiple times by mistake.


Even if there is no problem right now, the code is more difficult to review and a simple refactoring can create a bug. For example the lifetime of the event publisher could change and prevent subscribers from being garbage collected.


There are patterns to automatically unsubscribe, but the simplest and most readable solution remains to unsubscribe from events explicitly using ``++-=++``.


This rule raises an issue when a class subscribes to an even using ``+++=++`` without explicitly unsubscribing with ``++-=++``.
