>perl -wMstrict -le
"use diagnostics;
 ;;
 my %hash = { foo => 'bar' };
"
Reference found where even-sized list expected at -e line 1 (#1)
    (W misc) You gave a single reference where Perl was
    expecting a list with an even number of elements (for
    assignment to a hash).  This usually means that you
    used the anon hash constructor when you meant to use
    parens. In any case, a hash requires key/value pairs.
        %hash = { one => 1, two => 2, };        # WRONG
        %hash = [ qw/ an anon array / ];        # WRONG
        %hash = ( one => 1, two => 2, );        # right
        %hash = qw( one 1 two 2 );              # also fine