golang：Go語言對象到C++類

《GO語言高級編程》設計中案例，僅作爲筆記進行收藏。要實現Go語言對象到C++類的包裝需要經過以下幾個步驟：首先是將Go對象映射爲一個id；然後基於id導出對應的C接口函數；最後是基於C接口函數包裝爲C++對象。

• 構造一個Go對象

// persion.go
package main

type Person struct {
	name string
	age  int
}

func NewPerson(name string, age int) *Person {
	return &Person{
		name: name,
		age:  age,
	}
}

func (p *Person) Set(name string, age int) {
	p.name = name
	p.age = age
}

func (p *Person) Get() (name string, age int) {
	return p.name, p.age
}

• 導出C接口

// person_capi.h
#include <stdint.h>

typedef uintptr_t person_handle_t;

person_handle_t person_new(char* name, int age);
void person_delete(person_handle_t p);

void person_set(person_handle_t p, char* name, int age);
char* person_get_name(person_handle_t p, char* buf, int size);
int person_get_age(person_handle_t p);

// goobj.go

package main

import (
	"sync"
)

type ObjectId int32

var refs struct {
	sync.Mutex
	objs map[ObjectId]interface{}
	next ObjectId
}

func init() {
	refs.Lock()
	defer refs.Unlock()

	refs.objs = make(map[ObjectId]interface{})
	refs.next = 1000
}

func NewObjectId(obj interface{}) ObjectId {
	refs.Lock()
	defer refs.Unlock()

	id := refs.next
	refs.next++

	refs.objs[id] = obj
	return id
}

func (id ObjectId) IsNil() bool {
	return id == 0
}

func (id ObjectId) Get() interface{} {
	refs.Lock()
	defer refs.Unlock()

	return refs.objs[id]
}

func (id ObjectId) Free() interface{} {
	refs.Lock()
	defer refs.Unlock()

	obj := refs.objs[id]
	delete(refs.objs, id)

	return obj
}

// person_capi.go
package main

//#include "./person_capi.h"
import "C"
import "unsafe"

//export person_new
func person_new(name *C.char, age C.int) C.person_handle_t {
	id := NewObjectId(NewPerson(C.GoString(name), int(age)))
	return C.person_handle_t(id)
}

//export person_delete
func person_delete(h C.person_handle_t) {
	ObjectId(h).Free()
}

//export person_set
func person_set(h C.person_handle_t, name *C.char, age C.int) {
	p := ObjectId(h).Get().(*Person)
	p.Set(C.GoString(name), int(age))
}

//export person_get_name
func person_get_name(h C.person_handle_t, buf *C.char, size C.int) *C.char {
	p := ObjectId(h).Get().(*Person)
	name, _ := p.Get()

	n := int(size) - 1
	bufSlice := ((*[1 << 31]byte)(unsafe.Pointer(buf)))[0:n:n]
	n = copy(bufSlice, []byte(name))
	bufSlice[n] = 0

	return buf
}

//export person_get_age
func person_get_age(h C.person_handle_t) C.int {
	p := ObjectId(h).Get().(*Person)
	_, age := p.Get()
	return C.int(age)
}

• 封裝C++對象

// person.h
extern "C" {
	#include "./person_capi.h"
}

struct Person {
	static Person* New(const char* name, int age) {
		return (Person*)person_new((char*)name, age);
	}
	void Delete() {
		person_delete(person_handle_t(this));
	}

	void Set(char* name, int age) {
		person_set(person_handle_t(this), name, age);
	}
	char* GetName(char* buf, int size) {
		return person_get_name(person_handle_t(this), buf, size);
	}
	int GetAge() {
		return person_get_age(person_handle_t(this));
	}
};

// person.cc
#include "person.h"

• 運行

// main.cc
#include "person.h"

#include <stdio.h>

extern "C" void Main() {
	auto p = Person::New("gopher", 10);

	char buf[64];
	char* name = p->GetName(buf, sizeof(buf)-1);
	int age = p->GetAge();

	printf("%s, %d years old.\n", name, age);
	p->Delete();
}

// main.go

package main

// #cgo CXXFLAGS: -std=c++11
// extern void Main();
import "C"

func main() {
	C.Main()
}