Re^3: Getting Getopt::Long values into a hash

It seems that you must have $my_hash as a hashref, rather than having a %my_hash. The arrow-form adds a dereference to the LHS value. In my example, #1 and #2 are equivalent:

my $ref = { foo => "bar" };

print ${$ref}{"foo"};  #1  prints "bar"
print $ref->{"foo"};   #2  prints "bar"
print $ref{"foo"};     #3  prints ""
      # and under strictures throws a: 
      # "Global symbol "%ref" requires explicit package name"
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$ref{"foo"} only returns a value if there is a hash named %ref.

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Re^4: Getting Getopt::Long values into a hash by jeanluca (Deacon) on Nov 08, 2005 at 15:21 UTC
I almost start my script with: my $my_hash = {} ; As far as I know this should create a hash reference ?! What exactly means 'dereference to the LHS value' ? When it comes to variables and references I often get confused! Thnx Luca	[reply]
Re^5: Getting Getopt::Long values into a hash by fishbot_v2 (Chaplain) on Nov 08, 2005 at 16:01 UTC
As far as I know this should create a hash reference Yes that is correct. What exactly means 'dereference to the LHS value'? LHS = left hand side. I meant that the arrow operator takes a reference on the left, and dereferences it (ie. 'replaces' it with what it points to). You can then subscript it in various ways, with a key (for a hashref), an index (arrayref), parameters (coderef), or a method (object). A hashref is not a hash, and thus you cannot access it directly. You need to first "fetch" the hash that it points to.	[reply]
Re^6: Getting Getopt::Long values into a hash by jeanluca (Deacon) on Nov 08, 2005 at 16:51 UTC
Thanks a lot, I just wrote a short test program: `#! /usr/bin/perl my %mh ; $mh{a} = "b" ; $mh->{b} = "c" ; print "values are hash=$mh{a}, hash=$mh{b} or hashref=$mh->{b} \n" ;` [download] The problem with perl I think is that different types can have the same name. I wrote a script once, and before I knew it I was mixing hashes and hash references! Luca	[reply] [d/l]