%hash = ( key => "value" );

##</code><code>##

%hash = { key => "value" };

##</code><code>##

perl -MData::Dumper -wE 'my %fields = { id => 0, name => 1, age => 2}; say Dumper \%fields;'
Reference found where even-sized list expected at -e line 1.
$VAR1 = {
          'HASH(0x7f9d5a804850)' => undef
        };