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: clone.go
    path of file: ./repos/devspace/vendor/github.com/gogo/protobuf/proto
    
    the code of the file until where you have to start completion: // Go support for Protocol Buffers - Google's data interchange format
//
// Copyright 2011 The Go Authors.  All rights reserved.
// https://github.com/golang/protobuf
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// Protocol buffer deep copy and merge.
// TODO: RawMessage.

package proto

import (
	"fmt"
	"log"
	"reflect"
	"strings"
)

// Clone returns a deep copy of a protocol buffer.
func Clone(src Message) Message {
	in := reflect.ValueOf(src)
	if in.IsNil() {
		return src
	}
	out := reflect.New(in.Type().Elem())
	dst := out.Interface().(Message)
	Merge(dst, src)
	return dst
}

// Merger is the interface representing objects that can merge messages of the same type.
type Merger interface {
	// Merge merges src into this message.
	// Required and optional fields that are set in src will be set to that value in dst.
	// Elements of repeated fields will be appended.
	//
	// Merge may panic if called with a different argument type than the receiver.
	Merge(src Message)
}

// generatedMerger is the custom merge method that generated protos will have.
// We must add this method since a generate Merge method will conflict with
// many existing protos that have a Merge data field already defined.
type generatedMerger interface {
	XXX_Merge(src Message)
}

// Merge merges src into dst.
// Required and 
    
func mergeAny(out, in reflect.Value, viaPtr bool, prop *Properties) {
	if in.Type() == protoMessageType {
		if !in.IsNil() {
			if out.IsNil() {
				out.Set(reflect.ValueOf(Clone(in.Interface().(Message))))
			} else {
				Merge(out.Interface().(Message), in.Interface().(Message))
			}
		}
		return
	}
	switch in.Kind() {
	case reflect.Bool, reflect.Float32, reflect.Float64, reflect.Int32, reflect.Int64,
		reflect.String, reflect.Uint32, reflect.Uint64:
		if !viaPtr && isProto3Zero(in) {
			return
		}
		out.Set(in)
	case reflect.Interface:
		// Probably a oneof field; copy non-nil values.
		if in.IsNil() {
			return
		}
		// Allocate destination if it is not set, or set to a different type.
		// Otherwise we will merge as normal.
		if out.IsNil() || out.Elem().Type() != in.Elem().Type() {
			out.Set(reflect.New(in.Elem().Elem().Type())) // interface -> *T -> T -> new(T)
		}
		mergeAny(out.Elem(), in.Elem(), false, nil)
	case reflect.Map:
		if in.Len() == 0 {
			return
		}
		if out.IsNil() {
			out.Set(reflect.MakeMap(in.Type()))
		}
		// For maps with value types of *T or []byte we need to deep copy each value.
		elemKind := in.Type().Elem().Kind()
		for _, key := range in.MapKeys() {
			var val reflect.Value
			switch elemKind {
			case reflect.Ptr:
				val = reflect.New(in.Type().Elem().Elem())
				mergeAny(val, in.MapIndex(key), false, nil)
			case reflect.Slice:
				val = in.MapIndex(key)
				val = reflect.ValueOf(append([]byte{}, val.Bytes()...))
			default:
				val = in.MapIndex(key)
			}
			out.SetMapIndex(key, val)
		}
	case reflect.Ptr:
		if in.IsNil() {
			return
		}
		if out.IsNil() {
			out.Set(reflect.New(in.Elem().Type()))
		}
		mergeAny(out.Elem(), in.Elem(), true, nil)
	case reflect.Slice:
		if in.IsNil() {
			return
		}
		if in.Type().Elem().Kind() == reflect.Uint8 {
			// []byte is a scalar bytes field, not a repeated field.

			// Edge case: if this is in a proto3 message, a zero length
			// bytes field is considered the zero value, and should not
			// be merged.
			if prop != nil && prop.proto3 && in.Len() == 0 {
				return
			}

			// Make a deep copy.
			// Append to []byte{} instead of []byte(nil) so that we never end up
			// with a nil result.
			out.SetBytes(append([]byte{}, in.Bytes()...))
			return
		}
		n := in.Len()
		if out.IsNil() {
			out.Set(reflect.MakeSlice(in.Type(), 0, n))
		}
		switch in.Type().Elem().Kind() {
		case reflect.Bool, reflect.Float32, reflect.Float64, reflect.Int32, reflect.Int64,
			reflect.String, reflect.Uint32, reflect.Uint64:
			out.Set(reflect.AppendSlice(out, in))
		default:
			for i := 0; i < n; i++ {
				x := reflect.Indirect(reflect.New(in.Type().Elem()))
				mergeAny(x, in.Index(i), false, nil)
				out.Set(reflect.Append(out, x))
			}
		}
	case reflect.Struct:
		mergeStruct(out, in)
	default:
		// unknown type, so not a protocol buffer
		log.Printf("proto: don't know how to copy %v", in)
	}
}