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$MyApp::once{x} ||= 1;

sub f {
  ...
  log('some information'); # but should be called only the first time.
  ...
}

  static LogRetType const once=log('some information');

my $once1=0;
sub f {
...
  $once1 ||= (log('some information'),1);
  ...
}

sub f {
   ...
   $MyApp{+__FILE__.' '.__LINE__} ||= (log('some information'),1);
   ...
}