in reply to Re^2: Correct idiom for default parameters
in thread Correct idiom for default parameters

This is 5.8 accessible and might even be more palatable?

Updated per LanX's correction below. 

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

test();;
p1:1; p2:2; p3:3

test( 'a' );;
p1:a; p2:2; p3:3

test( 'a', 'b', 'c' );;
p1:a; p2:b; 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.
RIP an inspiration; A true Folk's Guy

Replies are listed 'Best First'.
Re^4: Correct idiom for default parameters
by LanX (Saint) on Apr 28, 2010 at 22:50 UTC
    careful!

    passing undef in between will break your idiom.

    IMHO better check scalar @_ or care explicitly about passing undef !

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

    [download]

    Cheers Rolf

[reply]
[d/l]
[select]

      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

      [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.
[reply]
[d/l]
        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');

        [download]

        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

[reply]
[d/l]
[select]

In Section Seekers of Perl Wisdom