[erlang-questions] Define "exists".

[Jon Watte]

Why do they need to be atoms?

We have a very similar case, where we take HTTP headers from calls to our
own servers and turn them into proplists, with atoms for the header kinds
("content-type," "cache-control" etc).
However, we'd probably be just as well off, if not better, to use binaries
as the keys -- we get those straight out of the HTTP request anyway. Then we
don't have the problem of growing atom store, and/or having to pre-declare
all possible headers we might care about.

Sincerely,

jw


--
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On Thu, Oct 13, 2011 at 6:24 AM, Eric Newhuis (personal) <enewhuis@REDACTED
> wrote:

> The problem is with list_to_existing_atom/1.  Really it is a great idea.
>  But...
>
> 1.  I have raw query strings coming in from the cruel outside world.
> 2.  I convert some bits of those into atoms by way of list_to_existing_atom
> so that someone cannot kill me with DOS attack by bloating my atom table.
> 3.  With me so far?  Good.
> 4.  My server, an OTP app, has a .app file that lists several other apps.
> 5.  list_to_existing_atom fails on atoms defined in those several other
> apps.
>
> Suggestion:  The documentation should specify what "exists" really means.
>
> Question:  What should I do to force the atoms from my dependent apps to be
> loaded?  I've been manually calling Module:module_info/0 just in time but,
> alas, this is starting to fail due to other module dependencies that are
> unknown at my call sites.
>
> For reference, here is the existing Erlang doc from the .org site:
>
> http://www.erlang.org/doc/man/erlang.html#list_to_existing_atom-1
>
> list_to_existing_atom(String) -> atom()
>
> Types:
>  String = string()
>
> Returns the atom whose text representation is String, but only if there
> already exists such atom.
>
> Failure: badarg if there does not already exist an atom whose text
> representation is String.
>
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