deep_merge.txt

Compare this lookup:
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# nodes/rizzo.puppetlabs.vm
---
hashme::myhash:
  flarghies:
    smarghies:
      - 'a'
      - 'b'

# common.yaml
---
hashme::myhash:
  flarghies:
    smarghies:
      - 'b'
      - 'c'
    klarghies:
      - 'f'

# hashme/manifests/init.pp
class hashme {
  $myhash = lookup({ "name"  => "hashme::myhash",
                     "merge" => "deep",
                   })
  notify { "${myhash}": }
}
------------->8------- cut here ------->8-------

To this deep_merge:
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$hishash = { 'flarghies' => { smarghies => ['a','b'] } }
$herhash = { 'flarghies' => {
               smarghies  => ['b','c'],
               'klarghies' => ['f']
              }
           }
$ourhash = deep_merge($hishash,$herhash)
notify { "${ourhash}": }
------------->8------- cut here ------->8-------