Variable behaving as a function call

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

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Re: Variable behaving as a function call by AnomalousMonk (Archbishop) on May 11, 2016 at 19:19 UTC
`c:\@Work\Perl\monks>perl -wMstrict -le "sub hiya { print 'hello there ', $_[0]; } hiya('sailor'); ;; my $coderef = hiya{CODE}; $coderef->('everybody'); " hello there sailor hello there everybody` [download] Update:* Please see `->` operator discussion The Arrow Operator in perlop; `*foo{THING}` discussion in Typeglobs and Filehandles in perldata. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^2: Variable behaving as a function call by ikegami (Patriarch) on May 11, 2016 at 19:31 UTC
`my $coderef = \&hiya;` is far more conventional, but both are ok for subroutines. Neither will work for operators such as `gmtime` and `localtime`, though. Since 5.16: `my $time_zone_func = $file =~ /^London/ ? \&CORE::gmtime : \&CORE::localtime; strftime($date_format, $time_zone_func->(time))` [download] Backwards compatible: `my $time_zone_func = $file =~ /^London/ ? sub { gmtime($_[0]) } : sub { localtime($_[0]) }; strftime($date_format, $time_zone_func->(time))` [download] or `my $time_zone_func = sub { $file =~ /^London/ ? gmtime($_[0]) : localtime($_[0]) }; strftime($date_format, $time_zone_func->(time))` [download]	[reply] [d/l] [select]
Re^3: Variable behaving as a function call by AnomalousMonk (Archbishop) on May 11, 2016 at 19:35 UTC
`... \&hiya;` is far more conventional ... Neither will work for operators such as `gmtime` ... Oops... Should've remembered that one! Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^2: Variable behaving as a function call by dirtdog (Monk) on May 11, 2016 at 19:23 UTC
works like a charm. Thanks!	[reply]
Re: Variable behaving as a function call by LanX (Saint) on May 11, 2016 at 19:39 UTC
Try `$time_zone_func = sub {gmtime()}; # then print $time_zone_func->(); # or print &$time_zone_func;` [download] Though in this case a normal named function seems to be the easiest approach. Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :) Je suis Charlie!}	[reply] [d/l]
Re: Variable behaving as a function call by BrowserUk (Patriarch) on May 11, 2016 at 19:44 UTC
If you are on Perl 5.16 or above, you can take references to most built-in functions, using the syntax: `\&CORE::builtin`. If you are on an earlier version, that isn't allowed, so you'd need to use wrappers: `$b = 0; $x = $b ? sub{ gmtime( @_ ) } : sub{ localtime( @_ ); }; print $x->( 123456 );; 1 0 0 1 0 70 4 0 0 $b = 1; $x = $b ? sub{ gmtime( @_ ) } : sub{ localtime( @_ ); }; print $x->( 123456 );; 1 0 0 1 0 70 4 0 0` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I knew I was on the right track :) In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re^2: Variable behaving as a function call by ikegami (Patriarch) on May 11, 2016 at 19:48 UTC
You need to replace `@_` with `$_[0]` because the argument is evaluated in scalar context.	[reply] [d/l] [select]
Re: Variable behaving as a function call by 1nickt (Canon) on May 11, 2016 at 19:44 UTC
Hi dirtdog, I believe you are looking for a CODEREF. You could do: `my $time_zone_func = ( $file =~ /^London/ ) ? sub { gmtime shift } : sub { localtime shift };` [download] to create a reference to an anonymous subroutine. You dereference the coderef with `&{ $ref }` so you would call it as: `$foo = &$time_zone_func( time );` [download] or `$bar = $time_zone_func->( time );` [download] Hope this helps! The way forward always starts with a minimal test.	[reply] [d/l] [select]