I can do this: : my $arr=[1,2,3]; but I can not do this : $arr[1] = 12; Neither this: my $y = {a=>1,b=>2}; $y['c'] = 3; All is forbidden!

I am assuming I have misunderstood your problem, but it seems to me, with what you've quoted, that your problem is irrelevant to Text::Xslate (which I know nothing about). If I try your code in pure perl, without Text::Xslate:

#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;

my $arr=[1,2,3];
$arr[1] = 12;           # Global symbol "@arr" requires explicit packa
+ge name (did you forget to declare "my @arr"?)

my $y = {a=>1,b=>2};
$y['c'] = 3;            # Global symbol "@y" requires explicit package
+ name (did you forget to declare "my @y"?)

print Data::Dumper->Dump([$arr, $y], [qw/arr y/]);
__END__
Global symbol "@arr" requires explicit package name (did you forget to
+ declare "my @arr"?) at C:\usr\local\share\PassThru\perl\perlmonks\11
+116710.pl line 7.
Global symbol "@y" requires explicit package name (did you forget to d
+eclare "my @y"?) at C:\usr\local\share\PassThru\perl\perlmonks\111167
+10.pl line 10.
Execution of C:\usr\local\share\PassThru\perl\perlmonks\11116710.pl ab
+orted due to compilation errors.
[download]

Since $arr is an array-ref and $y is a hash-ref, did you really mean the two assignments to be:

$arr->[1] = 12;
$y->{'c'} = 3;
[download]

because if I run the following modified, it works as expected:

#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;

my $arr=[1,2,3];
#$arr[1] = 12;           # Global symbol "@arr" requires explicit pack
+age name (did you forget to declare "my @arr"?)

my $y = {a=>1,b=>2};
#$y['c'] = 3;            # Global symbol "@y" requires explicit packag
+e name (did you forget to declare "my @y"?)

#print Data::Dumper->Dump([$arr, $y], [qw/arr y/]);

# did you really mean:
$arr->[1] = 12;
$y->{'c'} = 3;

print Data::Dumper->Dump([$arr, $y], [qw/arr y/]);
__END__
$arr = [
         1,
         12,
         3
       ];
$y = {
       'a' => 1,
       'c' => 3,
       'b' => 2
     };
[download]