prototypes parens/parenthesis hash initialization/declaration / Too many arguments for / $$

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I'm confused, I thought this would work

$ perl -MData::Dump -e " sub ff($$){ qq{@_} } my %f = ( 12 => ff 1,2, 
+34 => ff 3,4 ); dd\%f "
Too many arguments for main::ff at -e line 1, near "4 )"
Execution of -e aborted due to compilation errors.
[download]

without having to type parens like

$ perl -MData::Dump -e " sub ff($$){ qq{@_} } my %f = ( 12 => ff( 1,2)
+ , 34 => ff( 3,4) ); dd\%f "
{ 12 => "1 2", 34 => "3 4" }
[download]

A prototype of ($) doesn't require parens ... anyone?

Comment on prototypes parens/parenthesis hash initialization/declaration / Too many arguments for / $$ Select or Download Code

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Re: prototypes parens/parenthesis hash initialization/declaration / Too many arguments for / $$ by choroba (Cardinal) on Feb 12, 2013 at 09:48 UTC
Another reason why people should not use prototypes. They do not do what you think. See Are prototypes evil?. Update: BTW, the mentioned behaviour is normal: `$ perl -e 'print atan2 1, 2, 3' Too many arguments for atan2 at -e line 1, at EOF` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l]
Re^2: prototypes parens/parenthesis hash initialization/declaration / Too many arguments for / $$ by Anonymous Monk on Feb 12, 2013 at 09:52 UTC
Another reason why people should not use prototypes. They do not do what you think. See Are prototypes evil? Oh, context coersion gone amuch, icky I guess if that worked there wouldn't be a need for Devel::Declare and the like	[reply]
Re: prototypes parens/parenthesis hash initialization/declaration / Too many arguments for / $$ by AnomalousMonk (Archbishop) on Feb 12, 2013 at 18:12 UTC
Why not try a different approach? `>perl -wMstrict -MData::Dump -le "sub ff { return map { $_ => join ' ', m{ \d }xmsg } map { m{ \A \d{2} \z }xms ? $_ : die qq{bad arg: '$_'} } @_; } ;; my %f = ff(12, 34); dd \%f; " { 12 => "1 2", 34 => "3 4" }` [download]	[reply] [d/l]
Re: prototypes parens/parenthesis hash initialization/declaration / Too many arguments for / $$ by kcott (Archbishop) on Feb 12, 2013 at 21:57 UTC
"I'm confused, I thought this would work ..." Using `-MO=Deparse,-p` will show you how Perl parses the code and why it doesn't work: `$ perl -MO=Deparse,-p -e 'sub ff($$){ qq{@_} } my %f = ( 12 => ff 1,2, + 34 => ff 3,4 );' Too many arguments for main::ff at -e line 1, near "4 )" -e had compilation errors. sub ff ($$) { "@_"; } (my(%f) = (12, &ff(1, 2, 34, ff(3, 4))));` [download] On the last line of the output, you'll see `&ff(1, 2, 34, ff(3, 4))` has 4 arguments - your prototype specifies 2. -- Ken	[reply] [d/l] [select]