Can someone clarify what's happening here

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

This code:

@perls = (1, 2, 3, 4)
sub foo 
{
  my @foo = @{shift()};
  return join $/, @foo
}
print foo(\@perls)
[download]

Produces the following output:

one
two
three
four
[download]

however, if i change line 4 to:

my @foo = @{shift};
[download]

no output is produced after running. How exactly is @{shift()} being passed the contents of @_? At the moment this looks like witchcraft to me but I'd really like to know how this works.
Thanks,

Comment on Can someone clarify what's happening here Select or Download Code

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Re: Can someone clarify what's happening here by toolic (Bishop) on Aug 11, 2010 at 01:41 UTC
If you use warnings, you'll have your answer. See use strict and warnings.	[reply]
Re^2: Can someone clarify what's happening here by duranain (Initiate) on Aug 11, 2010 at 02:03 UTC
use strict causes it to whinge that i'm not using my to declare @perls, but if that's fixed, the code still exhibits the same behavior (@{shift()} works, @{shift} does not)	[reply]
Re^3: Can someone clarify what's happening here by ikegami (Patriarch) on Aug 11, 2010 at 02:20 UTC
Did you forgot to remove the parens? You should have gotten a warning and a strict error, but of which explain the issue. `use strict; use warnings; my @perls = (1, 2, 3, 4); sub foo { my @foo = @{shift}; return join $/, @foo } print foo(\@perls)` [download] `Ambiguous use of @{shift} resolved to @shift at a.pl line 7. Global symbol "@shift" requires explicit package name at a.pl line 7. Execution of a.pl aborted due to compilation errors.` [download]	[reply] [d/l] [select]
Re: Can someone clarify what's happening here by derby (Abbot) on Aug 11, 2010 at 10:21 UTC
Sometimes, the use of B::Deparse is helpful: `> perl -MO=Deparse script_1.pl my(@perls) = (1, 2, 3, 4); sub foo { my(@foo) = @{shift @_;}; return join($/, @foo); } print foo(\@perls); script_1.pl syntax OK > perl -MO=Deparse script_2.pl my(@perls) = (1, 2, 3, 4); sub foo { my(@foo) = @shift; return join($/, @foo); } print foo(\@perls); script_2.pl syntax OK` [download] -derby	[reply] [d/l]
Re: Can someone clarify what's happening here by biohisham (Priest) on Aug 11, 2010 at 09:07 UTC
The braces around the prefixes can be done away in this case, so `@{array}` is the same as `@array`, `${val}` is the same as `$val`. And this is why `@{shift}` is made to be an array whose name can also be written as `@shift` and of course array is not related to the function `shift()`. Excellence is an Endeavor of Persistence. A Year-Old Monk :D .	[reply] [d/l] [select]