Generic Iterator interface and MongoDB implementation

iterator.go

package iterator

type Iterator interface {
	Next() (value interface{}, done bool, err error)
}

mongodb.go

package mongodb

type iter struct {
	done, closed bool
	iter         *mgo.Iter
	result       func() interface{}
}

func (i *iter) Next() (interface{}, bool, error) {

	if !i.done {

		// Get a new instance.
		r := i.result()

		// Get the next value and return it.
		i.done = !(i.iter.Next(r))
		return r, i.done, nil
	}

	if !i.closed {
		i.closed = true
		if err := i.iter.Close(); err != nil {
			return nil, true, err
		}
	}

	return nil, true, nil
}