Do latter keys in an hash assignment from an array always override earlier keys?

Question

Given this:

%h = (a => 3, b => 4, a => 5);

Imperically $h{a} == 5 holds true, but are there cases where $h{a} == 3 because of internal dictionary hashing or some other perl-internal behavior?

Another way to ask: Does perl guarantee to keep key-ordering the same when assigning an array to a hash, even in the event of a key collision?

Duplicates key entries are convenient for things like %settings = (%defaults, %userflags) so I can hard-code defaults but override with user supplied flags.

Answer 1

key-ordering in a hash appears quite random. That is you cannot guarantee that the hash when dumped or looked at will be in the same order as you assigned it (a => 3, b => 4, a => 5); it could be displayed as ( b => 4, a => 5).

Also, there are only two key values in your hash the collision simply overwrites the first:

use Data::Dumper;

my %h = (a => 3, b => 4, a => 5);

print Dumper(\%h);
$VAR1 = {
          'a' => 5,
          'b' => 4
        };

It took me only three tries to produce:

$VAR1 = {
          'b' => 4,
          'a' => 5
        };

Updating as @mob mentioned left to right is what I would assume the second (or nth) assignment of a value to a key will replace the previous value. In this case you are replacing the whole hash the left to right ordering would result in a hash with two elements the value of any duplicates would be the last key/value encountered.