How does GenServer (and any other use injections) overriding work from a metaprogramming standpoint?

Questions / Help
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1

Given that use GenServer calls for the injection of the AST constructed in the __using__ function of GenServer, and given that this call is typically placed quite early in the module, and there doesn’t seem to be obvious deferment of this call, why can I override the behaviour callbacks with my own implementations?

I understand that module level expressions are evaluated before macro expansion, but def is a macro, so I’m still a bit unclear here.

EDIT: Sorry just to clarify, I conflated behaviours and use, I’m updating in the main post so that future posted are not perturbed by this error on my part.

2

What behaviour do you intend to override?

3

That’s what defoverridable does:

Makes the given definitions in the current module overridable.

If the user defines a new function or macro with the same name and arity, then the overridable ones are discarded. Otherwise, the original definitions are used.

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4

Thanks, there was a missing piece to the picture I had.