in reply to Re^5: Correct idiom for default parameters
in thread Correct idiom for default parameters

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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Re^7: Correct idiom for default parameters
by BrowserUk (Patriarch) on Apr 28, 2010 at 23:24 UTC

    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

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