PHP usortで無名関数

gistfile1.php

$array = array(
  array(
      'name' => 'sato'
    , 'sales' => 100
  )
  , array(
      'name' => 'suzuki'
    , 'sales' => 200
  )
  , array(
      'name' => 'tanaka'
    , 'sales' => 50
  )
);

usort( $array, function( $a, $b ) {
  if ( $a['sales'] == $b['sales'] ) return 0;
  return ( $a['sales'] > $b['sales'] ) ? 1 : -1;
});