perl -MData::Dumper -E 'use constant {A => 1}; my %h = (A => 2); say Dumper \%h'
$VAR1 = {
          'A' => 2
        };

perl -MData::Dumper -E 'use constant {A => 1}; my %h = (A() => 2); say Dumper \%h'
$VAR1 = {
          '1' => 2
        };