一个神奇的类，用来封装消息数据，统一数据传递接口，从unity引擎源码拷贝而来。

#include <iostream>

#include <assert.h>

#include <crtdefs.h>

struct MessageData

{

	int type;

private:

	// Note: on Metro WinRT types cannot be located in union, so don't use union!

	intptr_t data;

public:

	MessageData ()

	{

		data = 0; type = 0;

	}

	template<class T>

	void SetData (T inData, int classId)

	{

		// Check if SetData is used instead of SetScriptingObjectData

		//assert (type !=-1);

		//assert (sizeof (T) > sizeof (data)); // increase the data size

		*reinterpret_cast<T*> (&data) = *reinterpret_cast<T*> (&inData);

		type = classId;

	}

	template<class T>

	T GetData ()

	{

		// Check if GetData is used instead of GetScriptingObjectData

		assert (type != -1);

		return *reinterpret_cast<T*> (&data);

	}

	intptr_t& GetGenericDataRef ()

	{

		// Check if GetGenericDataRef is used instead of GetScriptingObjectData

		assert (type != -1);

		return data;

	}

};

class test

{

public:

	test(int x)

	{

		m_date = x;

	}

	void print()

	{

		std::cout<<m_date<<std::endl;

	}

private:

	int m_date ;

};

int main()

{

	MessageData data;

	test t(4);

	data.SetData(&t, 2);

	test * tt = data.GetData<test*>();

	tt->print();

	return 0;

}