[erlang-questions] dict:from_list/1 fragility

[Matej Kosik]

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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]}])

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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
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