text: // test $size
  load('jstests/aggregation/extras/utils.js');
  
  c = db.server4899;
  c.drop();
  c.save({arr:[]});
  c.save({arr:[1]});
  c.save({arr:["asdf", "asdfasdf"]});
  c.save({arr:[1, "asdf", 1234, 4.3, {key:23}]});
  c.save({arr:[3, [31, 31, 13, 13]]});
  
  result = c.aggregate({$project: {_id: 0, length: {$size: "$arr"}}});
  assert.eq(result.toArray(), [{length:0},
                               {length:1},
                               {length:2},
                               {length:5},
                               {length:2}]);
  
  c.save({arr:231});
  assertErrorCode(c, {$project: {_id: 0, length: {$size: "$arr"}}}, 17124);
  