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From: Rainer Weikusat <rweikusat@mssgmbh.com>
Newsgroups: comp.lang.perl.misc
Subject: Re: [OT] scoping
Date: Mon, 16 Sep 2013 10:46:31 +0100
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David Harmon <source@netcom.com> writes:
> On Sun, 14 Jul 2013 17:34:50 +0200 in comp.lang.perl.misc, "Dr.Ruud"
> <rvtol+usenet@xs4all.nl> wrote,
>>On 14/07/2013 17:11, Tim McDaniel wrote:
>>> In article <i7haba-e8u.ln1@anubis.morrow.me.uk>,
>>> Ben Morrow  <ben@morrow.me.uk> wrote:
>>>> Quoth "Dr.Ruud" <rvtol+usenet@xs4all.nl>:
>>
>>>>>       qq{
>>>>>           SELECT
>>>>>               $columns_csv
>>>>>           FROM
>>>>>               $table
>>>>>           WHERE
>>>>>               id IN (@ids)  -- hundreds easily
>>>>
>>>> Please, someone tell your cow-orkers about placeholders...
>>>
>>> The classic "Bobby Tables" strip:
>>> http://xkcd.com/327/
>>
>>Yeah, also doesn't apply.
>>
>>See how I left out what @ids is. Now, in stead of assuming anything else 
>>again, assume that @ids can only contain numbers, and that each is 
>>between 1 and some maximum.
>
> Uhm, no.  When evaluating whether code is broken or not, you don't
> assume perfect flawless input.  You assume worst case malicious NSA
> type input.

The code is 'broken' when it doesn't process the data it is supposed to
process such that the intended result results from that. Eg, this

sub sum
{
    return $_[0] + $_[1];
}

is a function which will return the sum of its first two arguments
provided that both are numbers. It can be made to do something very much
different,

---------
package Ha;

use overload "+" => negate;

sub new
{
    return bless([], $_[0]);
}

sub negate
{
    return ~$_[1];
}

package main;

sub sum
{
    return $_[0] + $_[1];
}

print(sum(3, 4), "\n");
print(sum(Ha->new(), 4), "\n");
---------

but this doesn't mean 'sum is broken': The precondition 'first two
arguments are numbers' is not true for the second call, hence, the
postcondition won't necessarily be true afterwards.

Whether or not 'will be a number > 1' is a sensible precondition in a
given situtation would be a different question.