$ perl -M5.026 -e'
   my $x = 123; my \$y = \$x; say $y;
'
The experimental declared_refs feature is not enabled at -e line 2.

$ perl -M5.026 -e'
   use feature qw( declared_refs );
   my $x = 123; my \$y = \$x; say $y;
'
Declaring references is experimental at -e line 3.
Experimental aliasing via reference not enabled at -e line 3.

$ perl -M5.026 -e'
   use feature qw( refaliasing declared_refs );
   my $x = 123; my \$y = \$x; say $y;
'
Declaring references is experimental at -e line 3.
Aliasing via reference is experimental at -e line 3.
123

$ perl -M5.026 -e'
   use feature qw( refaliasing declared_refs );
   no warnings qw( experimental::refaliasing experimental::declared_refs );
   my $x = 123; my \$y = \$x; say $y;
'
123

$ perl -M5.026 -e'
   use experimental qw( refaliasing declared_refs );
   my $x = 123; my \$y = \$x; say $y;
'
123