// Return a copy of the array with falsy values removed
public function compact($collection=null) {
list($collection) = self::_wrapArgs(func_get_args(), 1);
$collection = self::_collection($collection);
$__ = new self;
return self::_wrap($__->select($collection, function($val) {
return (bool) $val;
}));
}
function($val) {
代码来自php underscore, 这个地方报错, 似乎不能做参数.