Re^4: Correct idiom for default parameters

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

Comment on Re^4: Correct idiom for default parameters Select or Download Code

Replies are listed 'Best First'.
Re^5: Correct idiom for default parameters by BrowserUk (Patriarch) on Apr 28, 2010 at 22:59 UTC
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. RIP an inspiration; A true Folk's Guy	[reply] [d/l]
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');` [download] `p1:a; p2:2; p3:3` $p3 ne 'c' the first undef value omits the shift, all following parameters will be replaced by defaults! You need an explicit shift after the colon! Cheers Rolf	[reply] [d/l] [select]
Re^7: Correct idiom for default parameters by BrowserUk (Patriarch) on Apr 28, 2010 at 23:24 UTC
Arg! You're right. I tried it against my 5.10 version, because it was sitting there at the command prompt: `sub test{ my($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` [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	[reply] [d/l]


Clear questions and runnable code get the best and fastest answer
	PerlMonks