/ 
Symbol-Get-0.10
River stage one • 2 direct dependents • 2 total dependents
/ Symbol::Get

NAME

Symbol::Get - Read Perl’s symbol table programmatically

SYNOPSIS

package Foo;

our $name = 'haha';
our @list = ( 1, 2, 3 );
our %hash = ( foo => 1, bar => 2 );

use constant my_const => 'haha';

sub doit { ... }

my $name_sr = Symbol::Get::get('$Foo::name');    # \$name
my $list_ar = Symbol::Get::get('$Foo::list');    # \@list
my $hash_hr = Symbol::Get::get('$Foo::hash');    $ \%hash

#Defaults to __PACKAGE__ if none is given:
my $doit_cr = Symbol::Get::get('&doit');

#A constant--note the lack of sigil.
#See below for important compatibility information!
my $const_sr = Symbol::Get::get('Foo::my_const');
my $const_ar = Symbol::Get::get('Foo::my_const_list');

#No compatibility issues here:
my $const_val = Symbol::Get::copy_constant('Foo::my_const');
my @const_list = Symbol::Get::copy_constant('Foo::my_const_list');

#The below return the same results since get_names() defaults
#to the current package if none is given.
my @names = Symbol::Get::get_names('Foo');      # keys %Foo::
my @names = Symbol::Get::get_names();

DESCRIPTION

Occasionally I have need to reference a variable programmatically. This module facilitates that by providing an easy, syntactic-sugar-y, read-only interface to the symbol table.

The SYNOPSIS above should pretty well cover usage.

ABOUT PERL CONSTANTS

In modern Perl versions this construction:

use constant foo => 'bar';

… does something rather special with the symbol table: while you access foo as though it were a function (e.g., foo(), or just bareword foo), the actual symbol table entry is a SCALAR reference, not a GLOB like other entries.

Symbol::Get::get() expects you to pass in names of constants WITHOUT trailing parens (()), as in the example above.

List constants are a bit more “interesting”. The following:

use constant things => qw( a b c );

… will, in Perl versions since 5.20, create an array reference in the symbol table, analogous to the scalar reference for a single value. Symbol::Get::get() will return a reference to that array.

It gets hairier: even in modern Perl, sometimes constants can be stored as CODE references. Compare the output of this one-liner …

perl -MData::Dumper -e'package foo; use constant haha => 7; print haha(); print Data::Dumper::Dumper(\%foo::);'

… to this one:

perl -MData::Dumper -e'package foo; print haha(); print Data::Dumper::Dumper(\%foo::); use constant haha => 7;'

So, to be perfectly safe in accessing constants, just use copy_constant().

LEGACY PERL VERSIONS

PRE-5.20: Perl versions prior to 5.20 stored list constants as code references. To fetch a list constant in pre-5.20 code you’ll need to fetch it as a coderef or with copy_constant(), as shown above.

PRE-5.10: Scalar AND list constants are stored as code references. So you’ll need to fetch all constants as code refs, or via copy_constant(), as shown above.

SEE ALSO

LICENSE

This module is licensed under the same license as Perl.