my $hash = { a => 'b' };
$hash->{$x}

##</code><code>##

my %hash = ( a => 'b' );
$hash{$x}

##</code><code>##

use strict;
use warnings;

use Benchmark qw( cmpthese );

{
   my $test_const_hr   = q{                                           my $e = $const_hr->{a};              };
   my $test_const_hash = q{                                           my $e = $const_hash{a};              };
   my $test_built_hr   = q{ my $built_hr   = { a => 'A', b => 'B' };  my $e = $built_hr->{a};              };
   my $test_built_hash = q{ my %built_hash = ( a => 'A', b => 'B' );  my $e = $built_hash{a};              };
   my $test_inline_hr  = q{                                           my $e = { a => 'A', b => 'B' }->{a}; };

   our $const_hr   = { a => 'A', b => 'B' };
   our %const_hash = ( a => 'A', b => 'B' );

   $_ = 'use strict; use warnings; our $const_hr; our %const_hash; ' . $_
      for $test_const_hr,
          $test_const_hash,
          $test_built_hr,
          $test_built_hash,
          $test_inline_hr;

   cmpthese(-3, {
      const_hr    => $test_const_hr,
      const_hash  => $test_const_hash,
      built_hr    => $test_built_hr,
      built_hash  => $test_built_hash,
      inline_hr   => $test_inline_hr,
   });
}

##</code><code>##

                Rate  inline_hr   built_hr built_hash   const_hr const_hash
inline_hr   209314/s         --        -3%       -27%       -87%       -90%
built_hr    216267/s         3%         --       -24%       -87%       -90%
built_hash  285632/s        36%        32%         --       -83%       -86%
const_hr   1638207/s       683%       657%       474%         --       -22%
const_hash 2103430/s       905%       873%       636%        28%         --