flattened-args

#!/usr/bin/perl
use strict;
use warnings;
use 5.010;

my $extrakey = "doot";
my $extraval = "toot";

my %hash = (
  name => 'Joe',
  age => 'Grumpy',
);

sub myFunction {
  my %hash = @_;

  say $hash{name};
  say $hash{doot};
  say $hash{age};
}

myFunction($extrakey, $extraval, %hash);

# This prints:
# Joe
# toot
# Grumpy

Everything gets flattened as it comes into the function.

Refs are the way to avoid that flattening (because a ref just points to data, it isn't the data so there's nothing to flatten), if you need to pass in complex data structures.