Why are behaviour methods referred to as "callbacks"?

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You have not yet used GenServers? They do it very similar to this…

Just to underline this point: example

The Demo module is the callback module. None of the usual behaviour ceremony is actually necessary - other than implementing the mandatory callback functions.

{:ok, pid} = GenServer.start_link(Demo,[])

The Demo callback module is composed with the GenServer behaviour module leading to a GenServer based process with the specialized Demo functionality.

In OO:

  • parse!/1 would be a method on the abstract class. It may have some generic logic but doesn’t do the actual work. It would call a hook method do_parse/1 that is left for the subclass to implement the content specific parsing.
  • The subclass overides do_parse/1 implementing the content specific implementation. You use the subclass to parse the content it is specialized for.

So:

  • Parser.parse!/2 is the generic function in the behaviour module that will delegate the details of parsing the specific content to MyParser.
  • MyParser is a collection of hook function implementations needed to parse the specific content (organized as a callback module).
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