> Mr.David,
> I have few questions:
> 1. What is the function of Scope Resolution Operator :: used
> in the code you sent me? (filter::$col[$i])
> 2. What are the arguments for the sub routine "filterspec"?
> you have put sub filterspec($@).
> 3. What is the output expected out of "map{ $e =~
> s/\b$_\b/filter::$_()/g } @col;"?
Hello.
Sorry about the Delay. My son was born Sunday and we've been
in and out of hospital for a week.
The 'scope resolution operator' in this case it FORCING the declaration
of all variables (x1, y1, y2 etc) to be in the 'filter' namespace..
This (a) prevents conflict with current local or global variables, and
(b) allows the 'filter_data' code to lock the filter expression into
the 'filter' namespace and prevent access to global variables or
functions (it does not do this thought. Doing so would be your
task. perldoc 'Safe' for more info)
The filterspec function tasks a 'code reference' and an array. Note
that
the '$@' is a prototype, and prototypes don't mean the same thing
to perl. Its really just means that there is a minimum of two
arguments
and no maximum.
The 'map' call takes the evaluation expression (in $e) and
does the following:
( x1 < 1000 ) && ( y1 > 30000 ) becomes (filter::x1() < 1000) &&
(filter::y1() > 30000)
Each element in '@col' is placed into '$_' and used to substitute '$_'
with 'filter::'$_'()'
So you see, it converts each reference to a column into a function call
which finds the data for that column. This is important, because
otherwise
the filter expression is not valid perl.
hope that helps.
Cheers.
>
>
> Can you please clarify me these things? Your kind help is solicited.
>
> Thanks
> Regards
> Guruguhan
> EACoE, India.
> * - *91-80-5031516
> * - *901-1516 ( Dial Com)
>
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