Binding two Perl hashes (not two anonymous hashes) - perl

Question

In order to reuse some already written code libraries, I need to "masquerade" a hash (%bar) into another hash (%foo) so that each changes made in %bar can be seen with %foo after their binding.
With an anonymous hash construct, it's easy: just copy the ref of bar into the ref of foo ( $foo = $bar; ).
How about "not using" an anonymous hash (because the code I have to reuse is built not using anonymous hash constructs) ? Is this only possible ?
Thanks.
use strict;
use Data::Dumper;
my %foo = ();
my %bar = ();
%foo = %bar; # This won't work as it copies %bar into %foo as at the current time.
$bar{A}->{st} = 'a';
$bar{A}->{qt} = 'a';
$bar{B}->{st} = 'b';
$bar{B}->{qt} = 'b';
# $foo{A}->{st} doesn't exist
Of course, an anonymous hash construct would have been a blessing.
use strict;
use Data::Dumper;
my $foo = {};
my $bar = {};
$foo = $bar; # This works fine.
$bar->{A}->{st} = 'a';
$bar->{A}->{qt} = 'a';
$bar->{B}->{st} = 'b';
$bar->{B}->{qt} = 'b';
print STDOUT "foo\n---\n";
print Dumper($foo) . "\n\n";
print STDOUT "bar\n---\n";
print Dumper($bar) . "\n\n";
Yields the expected result:
foo
---
$VAR1 = {
'B' => {
'st' => 'b',
'qt' => 'b'
},
'A' => {
'qt' => 'a',
'st' => 'a'
}
};
bar
---
$VAR1 = {
'B' => {
'st' => 'b',
'qt' => 'b'
},
'A' => {
'qt' => 'a',
'st' => 'a'
}
};

Answer 1

For your example, you can use Data::Alias to alias %bar to %foo. That allows you to make changes in %bar and later see those in %foo.
use strict;
use warnings;
use Data::Printer;
use Data::Alias;
my %foo = ();
my %bar = ();
alias %foo = %bar;
$bar{A}->{st} = 'a';
$bar{A}->{qt} = 'a';
$bar{B}->{st} = 'b';
$bar{B}->{qt} = 'b';
p %foo;
p %bar;
Output:
{
A {
qt "a",
st "a"
},
B {
qt "b",
st "b"
}
}
{
A {
qt "a",
st "a"
},
B {
qt "b",
st "b"
}
}