You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: packfile.go
    path of file: ./repos/devspace/vendor/gopkg.in/src-d/go-git.v4/plumbing/format/packfile
    
    the code of the file until where you have to start completion: package packfile

import (
	"bytes"
	"io"
	"os"

	billy "gopkg.in/src-d/go-billy.v4"
	"gopkg.in/src-d/go-git.v4/plumbing"
	"gopkg.in/src-d/go-git.v4/plumbing/cache"
	"gopkg.in/src-d/go-git.v4/plumbing/format/idxfile"
	"gopkg.in/src-d/go-git.v4/plumbing/storer"
)

var (
	// ErrInvalidObject is returned by Decode when an invalid object is
	// found in the packfile.
	ErrInvalidObject = NewError("invalid git object")
	// ErrZLib is returned by Decode when there was an error unzipping
	// the packfile contents.
	ErrZLib = NewError("zlib reading error")
)

// When reading small objects from packfile it is beneficial to do s
    
func (p *Packfile) GetByType(typ plumbing.ObjectType) (storer.EncodedObjectIter, error) {
	switch typ {
	case plumbing.AnyObject,
		plumbing.BlobObject,
		plumbing.TreeObject,
		plumbing.CommitObject,
		plumbing.TagObject:
		entries, err := p.EntriesByOffset()
		if err != nil {
			return nil, err
		}

		return &objectIter{
			// Easiest way to provide an object decoder is just to pass a Packfile
			// instance. To not mess with the seeks, it's a new instance with a
			// different scanner but the same cache and offset to hash map for
			// reusing as much cache as possible.
			p:    p,
			iter: entries,
			typ:  typ,
		}, nil
	default:
		return nil, plumbing.ErrInvalidType
	}
}