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構造体の値を別の構造体の値へコピーする

Last updated at Posted at 2014-10-02

メモ。

type Src struct {
	Name    string
	Age     uint16
	Address string
}

type Dst struct {
	Name string
	Age  uint16
}

例えば上のような2つの構造体があったとして

s := &Src{"A", 12, "Japan"}
d := new(Dst)
copyStruct(s, d)

fmt.Println(*d) // {A, 12}

みたいに、必要なフィールドだけ移すためのcopyStruct()関数を考える。

func copyStruct(src interface{}, dst interface{}) error {
	fv := reflect.ValueOf(src)
 
	ft := fv.Type()
	if fv.Kind() == reflect.Ptr {
		ft = ft.Elem()
		fv = fv.Elem()
	}
 
	tv := reflect.ValueOf(dst)
	if tv.Kind() != reflect.Ptr {
		return fmt.Errorf("[Error] non-pointer: %v", dst)
	}
 
	num := ft.NumField()
	for i := 0; i < num; i++ {
		field := ft.Field(i)
 
		if !field.Anonymous {
			name := field.Name
			srcField := fv.FieldByName(name)
			dstField := tv.Elem().FieldByName(name)
 
			if srcField.IsValid() && dstField.IsValid() {
				if srcField.Type() == dstField.Type() {
					dstField.Set(srcField)
				}
			}
		}
	}
 
	return nil
}
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