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Re^2: 5.26 sigil reference syntax in subfunction

by chenhonkhonk (Acolyte)
on Nov 01, 2017 at 17:19 UTC ( #1202538=note: print w/replies, xml ) Need Help??


in reply to Re: 5.26 sigil reference syntax in subfunction
in thread 5.26 sigil reference syntax in subfunction

What you wrote is not what I am doing. What you suggest produces errors, which I said in the original post: Omitting the ->%* produces an error "Experimental keys on scalar is now forbidden" and if I omit the leading % it says the global symbol $hash is not defined. ... After further testing, with the $${}{} assignment I can get the keys inside the function using %{ $$hash{'key'} } or $$hash{'key'}->%*

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Re^3: 5.26 sigil reference syntax in subfunction
by BillKSmith (Prior) on Nov 01, 2017 at 20:42 UTC
    kcott is actually suggesting that you follow rule 2 in Using References. This rule always works. All the other dereferencing rules are essentially shortcuts that work in special situations.
    Bill

      G'day Bill,

      ++ Thanks for posting that link.

      It's been quite some time since I read that, and had forgotten it was there; however, that does reflect what I was saying (plus examples, plus gotchas).

      — Ken

      Rule 2 case 3 is closest to what I am doing. The perlref page is pretty poor on explaining assigning values to subthings when the original value is a reference.

      Additionally, arrows can be omitted between brackets and braces EXCEPT when the first element is a reference (otherwise you must have $$ref{}{}thing or $ref->{}{}thing is a pretty glaring exception to "easier reading". Having ->% but not ->\% just adds to the complexity of when and which order symbols have to be used during referencing/dereferencing.

        The only advantage of rule 2 is that there are no exceptions. When I have a difficult reference problem, I solve it with rule 2, then simplify it with the other rules, testing each change as I make it. You did motivate me to read the reference document again. I find that the text of the rule is very clear. They probably should say that it can be applied recursively. I agree that the explanation (especially the examples) is confusing. I have created a few examples which I hope are more helpful. Each example shows the same thing using the variable and then the equivalent reference. I have used the test module to prove that they are the same.
        use strict; use warnings; use Test::Simple tests => 6; # Scalars my $x = 3; my $scalar_ref = \$x; ok( $x eq ${$scalar_ref}, 'EXAMPLE I'); my $scalar_ref_ref = \$scalar_ref; ok( $x eq ${${$scalar_ref_ref}}, 'EXAMPLE II' ); # Rule 2 recurrsiv +e # Array my @array = (0, 1, 2, 3); my $array_ref = \@array; ok( join( @array) eq join( @{$array_ref} ), 'EXAMPLE III' ); ok( $array[3] eq ${$array_ref}[3], 'EXAMPLE IV' ); # value = 3 # Array-0f-Arrays my @as = qw(a aa aaa aaaa); my @bs = qw(b bb bbb bbbb); my @cs = qw(c cc ccc cccc); my @ds = qw(d dd ddd dddd); my @AoA = (\@as, \@bs, \@cs, \@ds); ok( join( @ds ) eq join( @{$AoA[3]} ), 'EXAMPLE V' ); ok( $ds[3] eq ${$AoA[3]}[3], 'EXAMPLE VI' ); # value = 'dddd'
        Bill

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