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Re: Clobbered parameter names via DECLARE in PL/PgSQL

From: Brendan Jurd <direvus(at)gmail(dot)com>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Clobbered parameter names via DECLARE in PL/PgSQL
Date: 2012-04-15 08:24:27
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Lists: pgsql-hackers
On 15 April 2012 17:55, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
> 2012/4/15 Brendan Jurd <direvus(at)gmail(dot)com>:
>> It turns out that in a PL/PgSQL function, you can DECLARE a variable
>> using the same name as one of the function parameters.  This has the
>> effect of clobbering the parameter, for example:
>> I would suggest that if the user DECLAREs a variable with the same
>> name as a parameter, it is very evidently a programming error, and we
>> should raise the same "duplicate declaration" error.  I haven't yet
>> looked at how difficult this would be to fix, but if there are no
>> objections I would like to attempt a patch.
> I disagree - variables and parameters are in different namespace so
> you can exactly identify variable and parameter. More - it is
> compatibility break.

They may technically be in different namespaces, but the fact that the
declared variable quietly goes ahead and masks the parameter locally,
seems like a recipe for unexpected consequences.  It certainly was in
my case, and I doubt I'm the first or the last to make that mistake.

Under these conditions, you now have "foo" which refers to the
variable, and "" which refers to the parameter.
Not exactly a model of clarity, and it's also quite easy to miss the
part of the PL/PgSQL docs mentioning this notation.

Perhaps it's a failure of imagination on my part, but I can't think of
a legitimate reason for a programmer to deliberately use the same name
to refer to a declared variable and a function parameter.  What would
be the benefit?


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