原型模式（Prototype Pattern）与对象成员变量复制的问题
核心就是
clone()方法，返回Prototype对象的复制品。那么我们可能会这样进行对象的创建：新创建一个相同对象的实例，然后遍历原始对象的所有成员变量， 并将成员变量值复制到新对象中。这种方法的缺点很明显，那就是使用者必须知道对象的实现细节，导致代码之间的耦合。另外，对象很有可能存在除了对象本身以外不可见的变量，这种情况下该方法就行不通了。
package main
import (
"fmt"
"sync"
)
type clone interface {
clone() clone
}
type Message struct {
Header *Header
Body *Body
}
func (m *Message) clone() clone {
msg := *m
return &msg
}
type Header struct {
SrcAddr string
SrcPort uint64
DestAddr string
DestPort uint64
Items map[string]string
}
type Body struct {
Items []string
}
func GetMessuage() *Message {
return GetBuilder().
WithSrcAddr("192.168.0.1").
WithSrcPort(1234).
WithDestAddr("192.168.0.2").
WithDestPort(8080).
WithHeaderItem("contents", "application/json").
WithBodyItem("record1").
WithBodyItem("record2").Build()
}
type builder struct {
once *sync.Once
msg *Message
}
func GetBuilder() *builder {
return &builder{
once: &sync.Once{},
msg: &Message{
Header: &Header{},
Body: &Body{},
},
}
}
func (b *builder) WithSrcAddr(addr string) *builder {
b.msg.Header.SrcAddr = addr
return b
}
func (b *builder) WithSrcPort(port uint64) *builder {
b.msg.Header.SrcPort = port
return b
}
func (b *builder) WithDestAddr(addr string) *builder {
b.msg.Header.DestAddr = addr
return b
}
func (b *builder) WithDestPort(port uint64) *builder {
b.msg.Header.DestPort = port
return b
}
func (b *builder) WithHeaderItem(key, value string) *builder {
// 保证map只初始化一次
b.once.Do(func() {
b.msg.Header.Items = make(map[string]string)
})
b.msg.Header.Items[key] = value
return b
}
func (b *builder) WithBodyItem(record string) *builder {
// 保证map只初始化一次
b.msg.Body.Items = append(b.msg.Body.Items, record)
return b
}
func (b *builder) Build() *Message {
return b.msg
}
func main() {
msg := GetMessuage()
copy := msg.clone()
if copy.(*Message).Header.SrcAddr != msg.Header.SrcAddr {
fmt.Println("err")
} else {
fmt.Println("equal")
}
}