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mikl at linux-france.org
Posted: Thu Jun 24, 1999 4:52 pm Reply with quote
Guest
Hi,

I get a compile time error message when trying to use record_info/2 outside of the 'mnesia:create_table' context.

The error message is :
illegal record info

What I am trying to do is get the list of fields of an object :
(The aim of the function is to replace a fields value by its name, without specifically knowing what kind of record I am manipulating)

replace(Attr,Value, Obj) ->
%% Get record_name from Object
Record_name = element(1,Obj),
%% Get list of fields
List = record_info(fields, Record_name),
%% Get attribute position
%% +1 because of the table name at first position
Pos = pos(Attr,List) + 1,
case Pos of
0 ->
{error, attribute_does_not_exist_in_record};
N ->
Result = setelement(Pos, Obj, Value),
{ok,Result}
end.


Can you figure out what I am doing wrong or what I am misunderstanding ?


Thanks in advance for your help.

--
Mickael Remond
mikl_at_linux-france.org
ICQ : 2265396


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tobbe at serc.rmit.edu.au
Posted: Thu Jun 24, 1999 7:06 pm Reply with quote
Guest
> What I am trying to do is get the list of fields of an object :
> (The aim of the function is to replace a fields value by its name,
> without specifically knowing what kind of record I am manipulating)

> Record_name = element(1,Obj),
> %% Get list of fields
> List = record_info(fields, Record_name),

record_info/2 is resolved at compile time, so you can't do the above
(Remember, records is just syntactic sugar on top of tuples)

/Tobbe




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hakan at erix.ericsson.se
Posted: Mon Jun 28, 1999 5:51 am Reply with quote
Guest
On Fri, 25 Jun 1999, Torbjorn Tornkvist wrote:

>Date: Fri, 25 Jun 1999 05:05:53 +1000
>From: Torbjorn Tornkvist <tobbe_at_serc.rmit.edu.au>
>To: Mickael Remond <mikl_at_linux-france.org>
>Cc: erlang-questions_at_erlang.org
>Subject: Re: record_info/2
>
>
>> What I am trying to do is get the list of fields of an object :
>> (The aim of the function is to replace a fields value by its name,
>> without specifically knowing what kind of record I am manipulating)
>
>> Record_name = element(1,Obj),
>> %% Get list of fields
>> List = record_info(fields, Record_name),
>
>record_info/2 is resolved at compile time, so you can't do the above
>(Remember, records is just syntactic sugar on top of tuples)

If the table happens to be a Mnesia table, you may use the function
mnesia:table_info/2 instead of record_info/2:

.
.
TableName = element(1, Obj),
FieldList = mnesia:table_info(TableName, attributes),
.
.

mnesia:table_info/2 is resolved in run time.

/H
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