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variable processing and checking in one statement

by saunderson (Novice)
on Aug 06, 2012 at 22:09 UTC ( #985846=perlquestion: print w/ replies, xml ) Need Help??
saunderson has asked for the wisdom of the Perl Monks concerning the following question:

Hi all,

i wonder whether it's possible to simplify constructs like

doSthWith($test) if checkFn($test);
further, such that i have to write the variable ($test) only once!?

I often have to deal with such statements and i just don't want to use perl's default variable, so that it yields
$_=$test; doSthWith($_) if checkFn($_);
since $_ is often used by other statements in the same block.

How would you monks do it the neat way?

best regards

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Re: variable processing and checking in one statement
by BrowserUk (Pope) on Aug 06, 2012 at 22:26 UTC

    You could do:

    checkFn( $_ ) and doSthWith( $_ ) for $test;

    which wouldn't interfere with surrounding uses of $_; and avoids referencing $test twice.

    But I wouldn't unless the variable in question was a complex reference. Ie. a multi-level hash or array lookup.


    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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Re: variable processing and checking in one statement (for my)
by tye (Cardinal) on Aug 07, 2012 at 00:13 UTC
    for my $t ( $test ) { doWith($t) if check($t); }

    avoids $_ completely. Clearly not worth it if your variable is actually just $test.

    - tye        

      Thank you for your contribution. the for respectively the foreach approach will cetrainly find their ways in my future scripts ...
Re: variable processing and checking in one statement
by ig (Vicar) on Aug 07, 2012 at 04:37 UTC

    How about

    doSthWith(checkFn($test));

    Have checkFn return the passed data if all is well, or undef if not and have doSthWith check its arguments.

    Or, incorporate the check into doSthWith - depending on where you want to localize the knowledge about the condition, and how you want to handle the race between the check and what you do with $test

    And, I don't advocate this but find the range of possibilities interesting and can't seem to stop myself from updating:

    sub { doSthWith($_[0]) if(checkFn($_[0])); }->($test);

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