in reply to Re^4: Correct idiom for default parameters
in thread Correct idiom for default parameters

Sorry, I don't follow?

Passing undef gives exactly the effect I would expect and desire. That of accepting the default for that parameter: 

test( 'a', undef, 'c' );;
p1:a; p2:2; p3:c

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In the absence of evidence, opinion is indistinguishable from prejudice.
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Re^6: Correct idiom for default parameters
by LanX (Saint) on Apr 28, 2010 at 23:05 UTC
    well, thats not the result I get:

    sub defaults { 
    my( $p1, $p2, $p3) = map{ defined $_[0] ? shift : $_ }( 1, 2, 3 );
+ 
    print "p1:$p1; p2:$p2; p3:$p3\n"; 
};;
 
defaults('a', undef, 'c');

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    p1:a; p2:2; p3:3

    $p3 ne 'c'

    the first undef value omits the shift, all following parameters will be replaced by defaults! You need an explicit shift after the colon!

    Cheers Rolf

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      Arg! You're right. I tried it against my 5.10 version, because it was sitting there at the command prompt: 

      sub test{ 
    my($p1,$p2,$p3) = map shift // $_,(1,2,3); 
    print "p1:$p1; p2:$p2; p3:$p3"; 
};;

[0] Perl> test();;
p1:1; p2:2; p3:3

[0] Perl> test( 'a', 'b', 'c' );;
p1:a; p2:b; p3:c

[0] Perl> test( 'a', , 'c' );;
p1:a; p2:c; p3:3

[0] Perl> test( 'a', undef, 'c' );;
p1:a; p2:2; p3:c

      [download]
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
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