creating references

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

i was skimming through the camel book (just revising the long forgotten things) when something struck me.....
i made a small program that creates a reference to a scalar and a hash like this

use strict;
use warnings;
my $scalar_ref=*foo{SCALAR};
print "scalar ref defined\n" if defined $scalar_ref;
#------------------------#
my hash_ref=*foo{HASH};
print "hash ref defined\n" if defined hash_ref;
__END__
output
scalar ref defined
[download]

the output is right in this case as the compiler need not see a scalar to create a reference but it needs to see a hash to create a reference.... so for this i did

use strict;
use warnings;
my $scalar_ref=*foo{SCALAR};
print "scalar ref defined\n" if defined $scalar_ref;
#------------------------#
my %hash=();
my hash_ref=*hash{HASH};
print "hash ref defined\n" if defined hash_ref;
__END__
output
Name "main::foo" used only once: possible typo at ref.pl
Name "main::hash" used only once: possible typo at ref.pl
scalar defined
[download]

now the problem is... the compiler sees that we do hv a hash existing then too the statement hash ref defined doesnt crop up..... why is that????

=====================================================
i'am worst at what do best and for this gift i fell blessed...
i found it hard it's hard to find well whatever
NEVERMIND

Comment on creating references Select or Download Code

Replies are listed 'Best First'.
Re: creating references by BioLion (Curate) on Aug 21, 2009 at 08:38 UTC
Using diagnostics for more verbose warnings should make things more clear: Read more... (2 kB) The key part explaing the difference in ouput for your two scripts is : NOTE: This warning detects symbols that have been used only once so $c, @c, %c, c, &c, sub c{}, c(), and c (the filehandle or format) are considered the same; if a program uses $c only once but also uses any of the others it will not trigger this warning. There is also a good discussion of a similar problem in "main::Objects" used only once: possible typo. HTH. Just a something something...*	[reply] [d/l]
Re: creating references by ikegami (Patriarch) on Aug 22, 2009 at 04:05 UTC
`foo` is a typeglob, or glob for short. It is the part of the symbol table that holds the variables associated with a name. Since the symbol table contains the package variables, the variables a glob contains are package variables* (often called global variables). `my` creates lexical variables. They're stored in the current function's pad, not the symbol table.	[reply] [d/l] [select]
Re: creating references by AnomalousMonk (Archbishop) on Aug 21, 2009 at 17:13 UTC
Note also that you are creating a lexical variable with the `my %hash=();` statement, and the `foo{THING}` syntax applies only to package* variables; you get the '... "main::hash" used only once ...' message because there is no `%hash` package hash variable in existence.	[reply] [d/l] [select]
Re^2: creating references by hnd (Scribe) on Aug 22, 2009 at 03:40 UTC
thnx.... ===================================================== i'am worst at what do best and for this gift i fell blessed... i found it hard it's hard to find well whatever NEVERMIND	[reply]


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