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Re: Is this bad? (How can this be avoided?)

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On 11/29/11 02:17 PM, mike3 wrote:
> On Nov 28, 5:04 pm, Ian Collins<ian-n...@hotmail.com>  wrote:
>> On 11/29/11 12:16 PM, mike3 wrote:
>>
>>
>>
>>> On Nov 28, 3:16 pm, Leigh Johnston<le...@i42.co.uk>    wrote:
>>>> On 28/11/2011 21:44, mike3 wrote:
>>
>>>> <snip code>
>>
>>>>> What to do? Now one could, I suppose, change to Circle* circle = new
>>>>> Circle(35.0, 55.0, 25.0);, but then we need something to take care of
>>>>> the garbage. Adding a delete() in, say, the destructor for Drawing
>>>>> might work, but we make some assumptions that may or may not be true,
>>>>> i.e. one can break it by misusing it, e.g. if one does not use a new
>>>>> to get the parameter or one forgets that destroying drawing also
>>>>> destroys circle, etc. Is it a bad idea to rely on the user's
>>>>> understanding -- to me it doesn't seem so. What should be done?
>>
>>>> Easy: use std::vector<std::tr1::shared_ptr<Shape>    >    (pre C++11) or
>>>> std::vector<std::unique_ptr<Shape>    >    (C++11) instead or take a look at
>>>> the Boost "ptr" containers.
>>
>>> And should the function addShape() be upgraded to use shared_ptr?
>>
>>> And also, though this solves the "garbage collection" issue, it still
>>> seems
>>> the user needs to understand that they must pass an object that's on
>>> the heap,
>>> and that it will be lost when the Drawing object is gone. Is that OK?
>>
>> Most drawing libraries I've used work this way, the container "owns" the
>> drawable objects.  The simplest solution is to have the Drawing
>> destructor free all of the Shape objects it owns.  So they all assume
>> the drawable objects are on the heap.
>>
>> If you want something more complex, such as the same shape in more than
>> one drawing, then something like a shared_ptr is the solution.
>>
>
> So then the requirement of the user to have to explicitly heap
> allocate
> otherwise bad things could happen is okay?

It's certainly not uncommon.  See the Qt documentation for an example.

-- 
Ian Collins

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Is this bad? (How can this be avoided?) mike3 <mike4ty4@yahoo.com> - 2011-11-28 13:44 -0800
  Re: Is this bad? (How can this be avoided?) Leigh Johnston <leigh@i42.co.uk> - 2011-11-28 22:16 +0000
    Re: Is this bad? (How can this be avoided?) mike3 <mike4ty4@yahoo.com> - 2011-11-28 15:16 -0800
      Re: Is this bad? (How can this be avoided?) Ian Collins <ian-news@hotmail.com> - 2011-11-29 13:04 +1300
        Re: Is this bad? (How can this be avoided?) mike3 <mike4ty4@yahoo.com> - 2011-11-28 17:17 -0800
          Re: Is this bad? (How can this be avoided?) Ian Collins <ian-news@hotmail.com> - 2011-11-29 14:28 +1300
      Re: Is this bad? (How can this be avoided?) "MikeWhy" <boat042-nospam@yahoo.com> - 2011-11-28 19:17 -0600
      Re: Is this bad? (How can this be avoided?) Leigh Johnston <leigh@i42.co.uk> - 2011-11-29 14:12 +0000
  Re: Is this bad? (How can this be avoided?) Goran <goran.pusic@gmail.com> - 2011-11-29 00:06 -0800
  Re: Is this bad? (How can this be avoided?) jgk@panix.com (Joe keane) - 2011-11-30 17:43 +0000
    Re: Is this bad? (How can this be avoided?) "MikeWhy" <boat042-nospam@yahoo.com> - 2011-11-30 12:26 -0600
      Re: Is this bad? (How can this be avoided?) jgk@panix.com (Joe keane) - 2011-11-30 20:36 +0000
    Re: Is this bad? (How can this be avoided?) Leigh Johnston <leigh@i42.co.uk> - 2011-11-30 18:26 +0000

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