PHP-CPP开发扩展（五）

PHP-CPP是一个用于开发PHP扩展的C++库。本节讲解如何在C++中实现PHP类。

类和对象

类和对象

怎样在PHP-CPP里写出PHP的类呢？很简单，看下面的例子：
main.cpp

/**
 * User: 公众号: 飞鸿影的博客(fhyblog)
 * Date: 2018/7
 */
#include <time.h>
#include <phpcpp.h>

/**
 *  Counter class that can be used for counting
 */
class Counter : public Php::Base
{
private:
    /**
     *  The initial value
     *  @var    int
     */
    int _value = 0;

public:
    /**
     *  C++ constructor and destructor
     */
    Counter() = default;
    virtual ~Counter() = default;

    /**
     *  Update methods to increment or decrement the counter
     *  Both methods return the NEW value of the counter
     *  @return int
     */
    Php::Value increment() { return ++_value; }
    Php::Value decrement() { return --_value; }

    /**
     *  Method to retrieve the current counter value
     *  @return int
     */
    Php::Value value() const { return _value; }
    
    //类的静态成员函数
    static Php::Value gettime() {return time(NULL);}
};

/**
 *  Switch to C context to ensure that the get_module() function
 *  is callable by C programs (which the Zend engine is)
 */
extern "C" {
    /**
     *  Startup function that is called by the Zend engine 
     *  to retrieve all information about the extension
     *  @return void*
     */
    PHPCPP_EXPORT void *get_module() {
    
        // 必须是static类型，因为扩展对象需要在PHP进程内常驻内存
        static Php::Extension extension("helloworld", "1.0.0");
        
        //初始化导出类
        Php::Class<Counter> counter("Counter");
        
        //注册导出类的可访问普通函数
        counter.method<&Counter::increment> ("increment");
        counter.method<&Counter::decrement> ("decrement");
        counter.method<&Counter::value> ("value");
        
        //注册导出类的可访问静态函数
        counter.method<&Counter::gettime>("gettime");

        //注册导出类，使用右值引用方式，优化资源使用
        extension.add(std::move(counter));
		
        // 返回扩展对象指针
        return extension;
    }
}

首先，C++类必须继承自Php::Base；其次，当我们将类添加到扩展对象时，还必须指定要从PHP访问的所有方法；最后再注册导出类。

我们先测试：

/**
 * User: 公众号: 飞鸿影的博客(fhyblog)
 * Date: 2018/7
 */
$counter = new Counter;
echo 'result of increment() = '. $counter->increment() . PHP_EOL;
echo 'result of increment() = '. $counter->increment() . PHP_EOL;
echo 'result of decrement() = '. $counter->decrement() . PHP_EOL;
echo 'result of value() = '. $counter->value() . PHP_EOL;
echo 'result of gettime() = '. Counter::gettime() . PHP_EOL;

输出：

result of increment() = 1
result of increment() = 2
result of decrement() = 1
result of value() = 1
result of gettime() = 1531621728

访问修饰符

我们还可以对导出的方法添加访问修饰符：

//初始化导出类
Php::Class<Counter> counter("Counter");

//注册导出类的可访问普通函数
counter.method<&Counter::increment> ("increment", Php::Private, {
    Php::ByVal("a", Php::Type::Numeric)
});
counter.method<&Counter::decrement> ("decrement", Php::Protected, {
    Php::ByVal("a", Php::Type::Numeric)
});
counter.method<&Counter::value> ("value");

Php::Class::method第二个参数支持设置访问修饰符，默认是public；第三个参数和普通函数一样，支持设置参数类型。

支持的访问修饰符：

extern PHPCPP_EXPORT const int Static;
extern PHPCPP_EXPORT const int Abstract;
extern PHPCPP_EXPORT const int Final;
extern PHPCPP_EXPORT const int Public;
extern PHPCPP_EXPORT const int Protected;
extern PHPCPP_EXPORT const int Private;
extern PHPCPP_EXPORT const int Const;

有一点需要注意：C++里要导出的方法，必须全是Public的， 即使我们在PHP中将它们标记为私有或受保护。因为我们写的方法由PHP-CPP库调用，如果将它们设为私有，它们将对库不可见。

抽象类、Final类

声明类为Final很简单，只需要在初始化导出类的时候声明一下即可：

Php::Class<Counter> counter("Counter", Php::Final);

那么怎么声明一个抽象类呢？上面的例子里Php::Class::method都传入了真正的C ++方法的地址，但是抽象方法通常没有实现，那么我们需要怎么提供指向方法的指针？幸运的是，在PHP-CPP里注册抽象方法不用提供指向C ++方法的指针。

示例：
抽象类原申明：

/**
 * User: 公众号: 飞鸿影的博客(fhyblog)
 * Date: 2018/7
 */
#include <phpcpp.h>

//类声明
class MyAbstract : public Php::Base{};

extern "C" {
    
    PHPCPP_EXPORT void *get_module() 
    {
        // 必须是static类型，因为扩展对象需要在PHP进程内常驻内存
        static Php::Extension extension("helloworld", "1.0.0");
        
        //初始化导出类
        Php::Class<MyAbstract> my_abstract("MyAbstract", Php::Abstract);
        
        //注册抽象方法：如果不给出C++方法的地址，该方法自动变成抽象方法
        my_abstract.method("myAbstractMethod", { 
            Php::ByVal("a", Php::Type::String, true) 
        });
        
        extension.add(std::move(my_abstract));
		
        // 返回扩展对象指针
        return extension;
    }
}

我们在test.php尝试去实例化MyAbstract类，提示：

PHP Fatal error:  Uncaught Error: Cannot instantiate abstract class MyAbstract

注：官方示例里初始化导出类里没有加Php::Abstract,测试的时候发现还是可以实例化的，只是调用抽象方法才报错。

构造函数和析构函数

在C++代码里，PHP的构造函数和析构函数本质上是普通方法。明白了这点，就不难实现了。

示例：

/**
 * User: 公众号: 飞鸿影的博客(fhyblog)
 * Date: 2018/7
 */
#include <phpcpp.h>

/**
 *  Simple counter class
 */
class Counter : public Php::Base
{
private:
    /**
     *  Internal value
     *  @var int
     */
    int _value = 0;

public:
    /**
     *  c++ constructor
     */
    Counter() = default;

    /**
     *  c++ destructor
     */
    virtual ~Counter() = default;

    /**
     *  php "constructor"
     *  @param  params
     */
    void __construct(Php::Parameters &params)
    {
        // copy first parameter (if available)
        if (!params.empty()) _value = params[0];
    }

    /**
     *  functions to increment and decrement
     */
    Php::Value increment() { return ++_value; }
    Php::Value decrement() { return --_value; }
    Php::Value value() const { return _value; }
};

/**
 *  Switch to C context so that the get_module() function can be
 *  called by C programs (which the Zend engine is)
 */
extern "C" {
    /**
     *  Startup function for the extension
     *  @return void*
     */
    PHPCPP_EXPORT void *get_module() {
        static Php::Extension myExtension("my_extension", "1.0");

        // description of the class so that PHP knows which methods are accessible
        Php::Class<Counter> counter("Counter");
        counter.method<&Counter::__construct>("__construct");
        counter.method<&Counter::increment>("increment");
        counter.method<&Counter::decrement>("decrement");
        counter.method<&Counter::value>("value");

        // add the class to the extension
        myExtension.add(std::move(counter));

        // return the extension
        return myExtension;
    }
}

如果需要构造函数为私有的，只需要在注册的时候加个flag：

counter.method<&Counter::__construct>("__construct", Php::Private);

如果要禁止被clone，可以：

// alternative way to make an object unclonable
counter.method("__clone", Php::Private);

接口

接口(Interface)由于不需要具体方法的实现，我们可以通过与定义类的方式类似的方式来实现。唯一的区别是我们不使用Php::Class<YourClass>，而是一个Php::Interface实例。

//初始化
Php::Interface interface("MyInterface");

//添加成员方法
interface.method("myMethod", { 
    Php::ByVal("value", Php::Type::String, true) 
});

//注册到扩展
extension.add(std::move(interface));

继承

implement 实现

我们除了可以在PHP代码去实现接口或者继承类，也可以在C++里实现。该Php::Class<YourClass>对象有extends()和implements()，可用于指定基类和实现的接口。我们需要传入之前配置的类或接口。我们来看一个例子。

/**
 * User: 公众号: 飞鸿影的博客(fhyblog)
 * Date: 2018/7
 */
#include <phpcpp.h>
#include <iostream>

class MyClass : public Php::Base
{
    public:
        Php::Value myMethod(Php::Parameters &params){
            Php::out << "MyClass" << std::endl;
            return params;
        }
};

extern "C" {
    
    PHPCPP_EXPORT void *get_module() 
    {
        static Php::Extension extension("helloworld", "1.0.0");
        
        //定义接口
        Php::Interface interface("MyInterface");
        interface.method("myMethod", { 
            Php::ByVal("value", Php::Type::String, true) 
        });
        extension.add(std::move(interface));

        // 注册一个自定义类
        Php::Class<MyClass> myClass("MyClass");

        // 实现接口定义
        myClass.implements(interface);
        myClass.method<&MyClass::myMethod>("myMethod", {
            Php::ByVal("value", Php::Type::String, true) 
        });
        extension.add(std::move(myClass));

		
        // 返回扩展对象指针
        return extension;
    }
}

测试：

$obj = new MyClass();
var_dump($obj->myMethod(11));

extends 继承

PHP的继承与C++的继承没有直接关系，必须显示使用Php::Class::extends()进行继承。

还是接着上面的例子说明。

/**
 * User: 公众号: 飞鸿影的博客(fhyblog)
 * Date: 2018/7
 */
#include <phpcpp.h>
#include <iostream>

class MyClass : public Php::Base
{
    public:
        Php::Value myMethod(Php::Parameters &params){
            Php::out << "MyClass" << std::endl;
            return params;
        }
};

class MySubClass : public Php::Base{
};

extern "C" {
    
    PHPCPP_EXPORT void *get_module() 
    {
        static Php::Extension extension("helloworld", "1.0.0");
        
        //定义接口
        Php::Interface interface("MyInterface");
        interface.method("myMethod", { 
            Php::ByVal("value", Php::Type::String, true) 
        });
        

        // 注册一个自定义类
        Php::Class<MyClass> myClass("MyClass");

        // 实现接口定义
        myClass.implements(interface);
        myClass.method<&MyClass::myMethod>("myMethod", {
            Php::ByVal("value", Php::Type::String, true) 
        });
        
        Php::Class<MySubClass> mySubClass("MySubClass");
        mySubClass.extends(myClass);
        
        extension.add(std::move(interface));
        extension.add(std::move(mySubClass));
        extension.add(std::move(myClass));
		
        // 返回扩展对象指针
        return extension;
    }
}

注：注册类(extension.add)需要放到extends方法的后面，也就是不能先注册父类再使用extends，否则无法继承。建议实际编程的时候注册统一放到最后面。

魔术方法

在PHP-CPP里，仅__construct()需要显示的在get_module()里注册，其他的魔术方法像__get()、__set()、__call()、__toString()等都不需要注册。

#include <phpcpp.h>

/**
 *  A sample class, that has some pseudo properties that map to native types
 */
class User : public Php::Base
{
private:
    /**
     *  Name of the user
     *  @var    std::string
     */
    std::string _name;

    /**
     *  Email address of the user
     *  @var    std::string
     */
    std::string _email;

public:
    /**
     *  C++ constructor and C++ destructpr
     */
    User() = default;
    virtual ~User() = default;

    /**
     *  Get access to a property
     *  @param  name        Name of the property
     *  @return Value       Property value
     */
    Php::Value __get(const Php::Value &name)
    {
        // check if the property name is supported
        if (name == "name") return _name;
        if (name == "email") return _email;

        // property not supported, fall back on default
        return Php::Base::__get(name);
    }

    /**
     *  Overwrite a property
     *  @param  name        Name of the property
     *  @param  value       New property value
     */
    void __set(const Php::Value &name, const Php::Value &value) 
    {
        // check the property name
        if (name == "name") 
        {
            // store member
            _name = value.stringValue();
        }

        // we check emails for validity
        else if (name == "email")
        {
            // store the email in a string
            std::string email = value;

            // must have a '@' character in it
            if (email.find('@') == std::string::npos) 
            {
                // email address is invalid, throw exception
                throw Php::Exception("Invalid email address");
            }

            // store the member
            _email = email;
        }

        // other properties fall back to default
        else
        {
            // call default
            Php::Base::__set(name, value);
        }
    }

    /**
     *  Check if a property is set
     *  @param  name        Name of the property
     *  @return bool
     */
    bool __isset(const Php::Value &name) 
    {
        // true for name and email address
        if (name == "name" || name == "email") return true;

        // fallback to default
        return Php::Base::__isset(name);
    }

    /**
     *  Remove a property
     *  @param  name        Name of the property to remove
     */
    void __unset(const Php::Value &name)
    {
        // name and email can not be unset
        if (name == "name" || name == "email") 
        {
            // warn the user with an exception that this is impossible
            throw Php::Exception("Name and email address can not be removed");
        }

        // fallback to default
        Php::Base::__unset(name);
    }
    
    /**
     *  Overriden __call() method to accept all method calls
     *  @param  name        Name of the method that is called
     *  @param  params      Parameters that were passed to the method
     *  @return Value       The return value
     */
    Php::Value __call(const char *name, Php::Parameters &params)
    {
        // the return value
        std::string retval = std::string("__call ") + name;

        // loop through the parameters
        for (auto &param : params)
        {
            // append parameter string value to return value
            retval += " " + param.stringValue();
        }

        // done
        return retval;
    }
    
    /**
     *  Overriden __callStatic() method to accept all static method calls
     *  @param  name        Name of the method that is called
     *  @param  params      Parameters that were passed to the method
     *  @return Value       The return value
     */
    static Php::Value __callStatic(const char *name, Php::Parameters &params)
    {
        // the return value
        std::string retval = std::string("__callStatic ") + name;

        // loop through the parameters
        for (auto &param : params)
        {
            // append parameter string value to return value
            retval += " " + param.stringValue();
        }

        // done
        return retval;
    }

    /**
     *  Overridden __invoke() method so that objects can be called directly
     *  @param  params      Parameters that were passed to the method
     *  @return Value       The return value
     */
    Php::Value __invoke(Php::Parameters &params)
    {
        // the return value
        std::string retval = "invoke";

        // loop through the parameters
        for (auto &param : params)
        {
            // append parameter string value to return value
            retval += " " + param.stringValue();
        }

        // done
        return retval;
    }
    
    /**
     *  Cast to a string
     *  @return Value
     */
    Php::Value __toString()
    {
        return "abcd";
    }
};

/**
 *  Switch to C context to ensure that the get_module() function
 *  is callable by C programs (which the Zend engine is)
 */
extern "C" {
    /**
     *  Startup function that is called by the Zend engine 
     *  to retrieve all information about the extension
     *  @return void*
     */
    PHPCPP_EXPORT void *get_module() {

        // extension object
        static Php::Extension myExtension("my_extension", "1.0");

        // description of the class so that PHP knows 
        // which methods are accessible
        Php::Class<User> user("User");

        // add the class to the extension
        myExtension.add(std::move(user));

        // return the extension
        return myExtension;
    }
}

测试：

<?php
// initialize user and set its name and email address
$user = new User();
$user->name = "John Doe";
$user->email = "john.doe@example.com";

// show the email address
echo($user->email."
");

// remove the email address (this will cause an exception)
unset($user->email);
?>

（未完待续）

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