gistfile1.pp

define foo ($primary_interface='eth0') {
  notify { "foo $name local-scope":
    message => $primary_interface
  } ->

  notify { "foo $name top-scope":
    message => $::primary_interface
  }
}

class bar ($primary_interface='eth1') {
  notify { "bar local-scope":
    message => $primary_interface
  } ->

  notify { "bar top-scope":
    message => $::primary_interface
  }
}

foo { 'test1': } ->
foo { 'test2': primary_interface => 'eth1' } ->
class { 'bar': }

gistfile2.txt

Notice: Compiled catalog for puppet.localdomain in environment production in 0.07 seconds
Notice: eth0
Notice: /Stage[main]//Foo[test1]/Notify[foo test1 local-scope]/message: defined 'message' as 'eth0'
Notice: eth0
Notice: /Stage[main]//Foo[test1]/Notify[foo test1 top-scope]/message: defined 'message' as 'eth0'
Notice: eth1
Notice: /Stage[main]//Foo[test2]/Notify[foo test2 local-scope]/message: defined 'message' as 'eth1'
Notice: eth0
Notice: /Stage[main]//Foo[test2]/Notify[foo test2 top-scope]/message: defined 'message' as 'eth0'
Notice: eth1
Notice: /Stage[main]/Bar/Notify[bar local-scope]/message: defined 'message' as 'eth1'
Notice: eth0
Notice: /Stage[main]/Bar/Notify[bar top-scope]/message: defined 'message' as 'eth0'
Notice: Finished catalog run in 0.09 seconds