Re: [boost] auto_vector - vector with auto_ptr semantics

From: Rainer Deyke (root_at_[hidden])
Date: 2002-02-05 12:18:28

----- Original Message -----
From: "Howard Hinnant" <hinnant_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Tuesday, February 05, 2002 9:57 AM
Subject: Re: [boost] auto_vector - vector with auto_ptr semantics

> On Tuesday, February 5, 2002, at 11:38  AM, Peter Dimov wrote:
>
> > And let's not forget the 'other' move, that moves an object into
> > uninitialized memory (move1 and swap both require two objects to
operate
> > on.) std::vector needs this while reallocating.
>
> Yup!  A minimum of 2 types of move are absolutely necessary:
>
> 1.  Move construct.
> 2.  Move assign.
>
> One could argue that 2 more moves are useful:
>
> 3.  Move construct, destructing the source.
> 4.  Move assign, destructing the source.
>
> However 3 and 4 are very easily built on 1 and 2 by just calling the
> destructor on the source after the move.

Not necessarily: sometimes an object must hold resources to maintain
class invariants.   For example:

  class C {
  public:
    C() : fp(fopen("myfile", "rb")
    {
      if (!this->fp) throw something;
    }
    ~C()
    {
      fclose(fp); /* Do not check for null. */
    }
  private:
    FILE *fp;
  };

--
Rainer Deyke | root_at_[hidden] | http://rainerdeyke.com