[erlang-questions] dict:from_list/1 fragility

Matej Kosik <>
Mon Dec 17 22:11:28 CET 2007


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Friends,

I think there are two problems with the

	dict:from_list/1

function.

First: it is not trottel-fest (robust against my stupitidity). It lets me call it as follows:

	E = dict:from_list([{a,b},{c,d}]).

Instead of any kind of complain, it vigorously continues and binds E to an invalid dictionary. At
the first sight, things seem to be fine. This

	dict:fetch(a, E).

yields

	b

and this

	dict:fetch(c, E).

yields

	d

Hitherto everything seems fine. However, after I update the dictionary:

	F = dict:update(e, f, E).

and try to retrieve newly added element

	dict:fetch(e, F).

I get

	[f]

I have used dictionaries to store PIDs of processes, the dictionary is at the boot-time constructed
via dict:from_list/1 constructor and later it I call dict:append/3 function to get the richer
dictionary. However, this led to the situation that some values had

	pid()

"type" and others were of

	[pid()]

"type".

Do not you think that that the

	dict:from_list

should fail immediatelly if one calls it as I called it:

	dict:from_list([{a,b},{c,d}])

It should succeed only if the values are lists, such as

	dict:from_list([{a,[b]}, {c, [d]}])

- ----------------------------------------------------------------------------

Second: do not you think that the documentation should mention this fact?

I admit that I may be thinking in wrong (non-Erlang way) but this is how it seems to me.
- --
Matej Kosik
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFHZuYAL+CaXfJI/hgRArxNAJ9oZZ+wt9P1oJW4Gdqm+9B3zMSv9ACffqkP
J/aOAH/IzdX7FwxtQps6/TA=
=zzkM
-----END PGP SIGNATURE-----



More information about the erlang-questions mailing list