Comments on: Erlang lists:keyfind or proplists:get_value?

By: Richard Carlsson

Richard Carlsson — Sun, 05 Jun 2011 12:05:24 +0000

Hi Roberto. I know, but I recently started seeing tweets referring to this old blog article, and wanted to give newcomers some pointers.

By: Roberto Ostinelli

Roberto Ostinelli — Sun, 05 Jun 2011 10:27:19 +0000

hi richard, indeed.

btw, you are referring to erlang discussions which are one year younger than this very thread ;)

By: Richard Carlsson

Richard Carlsson — Sun, 05 Jun 2011 10:21:38 +0000

The proplists module is written in Erlang, while lists:keyfind/3 is implemented in C. The proplists module is mainly meant for situations like lists of user options, and lets you do things such as writing 'foo' to represent a tuple {foo,true}. Hence, it is a bit more complicated than keyfind/3. Typically, you'd use the proplists module to extract specific parameters from a list of options and then you'd store those parameters in a record for quick access within loops. It's reasonably efficient, considering the extra things that it does, but if you know that your lists contain only tagged tuples, it can be better to use lists:keyfind/3 and friends. See also: http://erlang.org/pipermail/erlang-patches/2011-May/002137.html and http://erlang.org/pipermail/erlang-patches/2011-May/002140.html.

By: Roberto Ostinelli

Roberto Ostinelli — Thu, 20 May 2010 14:57:27 +0000

thank you adam for this feedback.

yes, that is indeed true. what may be an additional reason, is that proplists:get_value performs additional tests on list size and key being an atom, all things which do slow down code.

By: Adam Kocoloski

Adam Kocoloski — Thu, 20 May 2010 14:46:52 +0000

Hi Roberto, keyfind and keysearch are BIFs, while proplists:get_value is not. We recently switched all internal KV lookups in CouchDB to use use keysearch (for R12 compatibility).