----- Original Message -----
From: "John W. Krahn" <[EMAIL PROTECTED]>
To: "Wiggins d Anconia" <[EMAIL PROTECTED]>; "Perl Beginners"
<[EMAIL PROTECTED]>
Sent: Friday, October 15, 2004 11:30 PM
Subject: Re: Reference syntax...
> Wiggins d Anconia wrote:
> >
> > Usually when you need this is when you have multiple depths of
> > references and the syntax becomes ambiguous to the interpreter.
> > Something like,
> >
> > @{$hashref->{$scalar}}
> >
> > In this case without the {} the interpreter can't tell if you mean,
>
> Yes, the interpreter can tell because of precedence. @$hashref->{$scalar}
is
> the same as @{$hashref}->{$scalar} which in this case will produce an
error.
>
> > (@$hashref) ->{$scalar} or @ ( $hashref->{$scalar} )
> >
> > The parens are NOT normal syntax, I am using them to show grouping.
>
> perldoc perldsc
> [snip]
> CAVEAT ON PRECEDENCE
> Speaking of things like "@{$AoA[$i]}", the following are actually
the
> same thing:
>
> $aref->[2][2] # clear
> $$aref[2][2] # confusing
>
> That's because Perl's precedence rules on its five prefix
dereferencers
> (which look like someone swearing: "$ @ * % &") make them bind more
> tightly than the postfix subscripting brackets or braces! This will
no
> doubt come as a great shock to the C or C++ programmer, who is quite
> accustomed to using *a[i] to mean what's pointed to by the i'th
element
> of "a". That is, they first take the subscript, and only then
deref-
> erence the thing at that subscript. That's fine in C, but this
isn't C.
>
> The seemingly equivalent construct in Perl, $$aref[$i] first does
the
> deref of $aref, making it take $aref as a reference to an array, and
then
> dereference that, and finally tell you the i'th value of the array
> pointed to by $AoA. If you wanted the C notion, you'd have to write
> "${$AoA[$i]}" to force the $AoA[$i] to get evaluated first before
the
> leading "$" dereferencer.
and just above it there is an interesting example...
for $i (1..10) {
@array = somefunc($i);
$AoA[$i] = [ @array ];
}
The square brackets make a reference to a new array with a *copy* of
what's in @array at the time of the assignment. This is what you want.
if one has a ref to HoH how would he make a copy of it using simular syntax
?? I know it can be done like this
use Storable qw(dclone);
my $HOH_REF_COPY = dclone($HOH_REF)
>
>
>
> John
> --
> use Perl;
> program
> fulfillment
>
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