Why do you think that that construct is illegal? I tried this code in perl 5.8.7 and it works without any warnings.

    use strict;
    use warnings;
    use Data::Dumper;
    my $a;
    %$a=(a=>1,b=>2);
    print Dumper($a);
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And it prints

    $VAR1 = {
              'a' => 1,
              'b' => 2
            };
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UPDATE : I see now that the illegal part was the "my %$h" part rather than the assigment part. So that could have been changed simply by splitting the declaration to a separate line, or by changing the list to a {}.

However it seems an odd way to do it when you could just say :

    $a={a=>1,b=>2};
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I benchmarked the two versions, and the first %$a=() is 50% slower than the second ($a={}).

Regarding the difference between $h{name} versus $h->{name}, there is a slight speed difference (10%), because the second version first needs to dereference $h before doing the lookup, but it is so blazingly fast that I wouldn't worry about it. (Tested on a small hash - not sure for bigger hashes)

Rather just use whatever is easier to read, as there are bound to be other bottlenecks that make much more difference to your code's performance.