merge.go

// Copyright 2013 Dario Castañé. All rights reserved.
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Based on src/pkg/reflect/deepequal.go from official
// golang's stdlib.

package mergo

import (
	"reflect"
)

// Traverses both values, assigning src's fields values to dst.
func deepMerge(dst, src reflect.Value, overwrite bool) (err error) {
	if !src.IsValid() {
		return
	}
	switch dst.Kind() {
	case reflect.Struct:
		for i, n := 0, dst.NumField(); i < n; i++ {
			if err = deepMerge(dst.Field(i), src.Field(i), overwrite); err != nil {
				return
			}
		}
	case reflect.Ptr:
		fallthrough
	case reflect.Interface:
		if src.IsNil() {
			break
		} else if dst.IsNil() || overwrite {
			if dst.CanSet() && (overwrite || isEmptyValue(dst)) {
				dst.Set(src)
			}
		} else if err = deepMerge(dst.Elem(), src.Elem(), overwrite); err != nil {
			return
		}
	default:
		if dst.CanSet() && !isEmptyValue(src) && (overwrite || isEmptyValue(dst)) {
			dst.Set(src)
		}
	}
	return
}

// Merge will fill any empty for value type attributes on the dst struct using corresponding
// src attributes if they themselves are not empty. dst and src must be valid same-type structs
// and dst must be a pointer to struct.
// It won't merge unexported (private) fields and will do recursively any exported field.
func Merge(dst, src interface{}) error {
	return merge(dst, src, false)
}

// MergeWithOverwrite will do the same as Merge except that non-empty dst attributes will be overriden by
// non-empty src attribute values.
func MergeWithOverwrite(dst, src interface{}) error {
	return merge(dst, src, true)
}

func merge(dst, src interface{}, overwrite bool) error {
	var (
		vDst, vSrc reflect.Value
		err        error
	)
	if vDst, vSrc, err = resolveValues(dst, src); err != nil {
		return err
	}
	if vDst.Type() != vSrc.Type() {
		return ErrDifferentArgumentsTypes
	}
	return deepMerge(vDst, vSrc, overwrite)
}