[erlang-questions] State of -extends(Module)?

Loïc Hoguin <>
Mon Oct 29 11:46:32 CET 2012

On 10/29/2012 11:36 AM, Magnus Müller wrote:
> In the never-ending quest of searching help to program as little as
> possible, I found Erlang's -extends(Module) directive. There is little
> documentation on it, which makes me believe that it is either
> an unwanted or not well-supported feature of the language. Is this
> correct? Would you recommend keeping away from it?

As a general rule, keep away from anything undocumented. They are either 
internal code (that may change at any time) or experimental features 
(that may be removed at any time).

I do not think it is used anywhere in OTP. I am not sure why it was 
added to the language. This looks like an experimental feature.

There was a discussion a few weeks back on how -extends changed in a 
recent version and made some code incompatible. Use at your own risk.

Loïc Hoguin
Erlang Cowboy
Nine Nines

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