【Boost】boost::noncopyable介绍 .

boost::noncopyable比较简单, 主要用于单例的情况.
通常情况下, 要写一个单例类就要在类的声明把它们的构造函数, 赋值函数, 析构函数, 复制构造函数隐藏到private或者protected之中, 每个类都这么做麻烦.
有noncopyable类, 只要让单例类直接继承noncopyable.
class noncopyable的基本思想是把构造函数和析构函数设置protected权限，这样子类可以调用，但是外面的类不能调用，那么当子类需要定义构造函数的时候不至于通不过编译。但是最关键的是noncopyable把复制构造函数和复制赋值函数做成了private，这就意味着除非子类定义自己的copy构造和赋值函数，否则在子类没有定义的情况下，外面的调用者是不能够通过赋值和copy构造等手段来产生一个新的子类对象的。

#ifndef BOOST_NONCOPYABLE_HPP_INCLUDED
#define BOOST_NONCOPYABLE_HPP_INCLUDED

namespace boost {

//  Private copy constructor and copy assignment ensure classes derived from
//  class noncopyable cannot be copied.

//  Contributed by Dave Abrahams

namespace noncopyable_  // protection from unintended ADL
{
  class noncopyable
  {
   protected:
      noncopyable() {}
      ~noncopyable() {}
   private:  // emphasize the following members are private
      noncopyable( const noncopyable& );
      const noncopyable& operator=( const noncopyable& );
  };
}

typedef noncopyable_::noncopyable noncopyable;

} // namespace boost

#endif  // BOOST_NONCOPYABLE_HPP_INCLUDED

#ifndef BOOST_NONCOPYABLE_HPP_INCLUDED
#define BOOST_NONCOPYABLE_HPP_INCLUDED

namespace boost {

//  Private copy constructor and copy assignment ensure classes derived from
//  class noncopyable cannot be copied.

//  Contributed by Dave Abrahams

namespace noncopyable_  // protection from unintended ADL
{
  class noncopyable
  {
   protected:
      noncopyable() {}
      ~noncopyable() {}
   private:  // emphasize the following members are private
      noncopyable( const noncopyable& );
      const noncopyable& operator=( const noncopyable& );
  };
}

typedef noncopyable_::noncopyable noncopyable;

} // namespace boost

#endif  // BOOST_NONCOPYABLE_HPP_INCLUDED

示例:

#include "tfun.h"

class myclass: public boost::noncopyable
{
public:
    myclass(){};
    myclass(int i){};
};

int main()
{
    myclass cl1();
    myclass cl2(1);

    // myclass cl3(cl1);    // error
    // myclass cl4(cl2);    // error

    return 0;
}