15.1. Callbacks and hooks
The use of callbacks and hooks is a fairly common meta-programming technique. These methods are called when a particular event takes place during the run of a Ruby program. An event is something like
- A nonexistent method being called on an object
- A module being mixed in to a class or another module
- An object being extended with a module
- A class being subclassed (inherited from)
- A reference being made to a nonexistent constant
- An instance method being added to a class
- A singleton method being added to an object
For every event in that list, you can (if you choose) write a callback method that will be executed when the event happens. These callback methods are per-object or per-class, not global; if you want a method ...
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