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POBest way to deal with object that can't instantiate itself?
 

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  1. POBest way to deal with object that can't instantiate itself?
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    <p>I guess I've asked a few similar questions before, but I was beating around the bush. I think this is the real problem that I can't quite lay to rest.</p> <p>I'm dealing with a <a href="http://www.box2d.org/" rel="nofollow noreferrer">third party library</a>, and there's an object that can't create itself, <code>b2Body</code>. The <code>b2World</code> has to <a href="http://programanddesign.com/box2d/classb2World.html#2eb36e967e43294bfa03ec3d177c2dae" rel="nofollow noreferrer">instantiate it</a>. I personally don't like this design pattern very much; I think the <code>b2Body</code> should be able to exist independently of the world, and then be added to the world when needed. Anyway, I've wrapped <code>b2Body</code> with my own class class, <code>Body</code>, because I need to add some extra stuff to it anyway. Similarly, I have a <code>World</code> wrapper. Now I figure I have 3 options:</p> <ol> <li>Have <code>Body</code>'s constructor takes a pointer to <code>World</code> so that it can be fully instantiated (calls <code>b2World::CreateBody</code> somewhere inside) -- i.e. have a constructor like <code>Body *b = new Body(world_ptr)</code></li> <li>Pass <code>Body</code> to some <code>World::CreateBody</code> method like how the library already does it -- i.e. <code>Body *b = world.CreateBody(params);</code></li> <li>Duplicate all the data in <code>b2Body</code> so that you can use it however you want, and then after you add it to the world it will 'switch over' to use the <code>b2Body</code> data -- i.e. <code>Body b</code> and later <code>world.addBody(b)</code>.</li> </ol> <p>(1) and (2) mean that you can't have a <code>Body</code> without a <code>World</code>, which I probably won't need, but it might be nice to have that option [so that I can use it as a template for other objects and such]. Not sure what other pros and cons there are. (3) seems nicer, but it's a lot more work to implement, and it means I have to duplicate most of the data that's already contained in <code>b2Body</code>.</p> <p>What are your thoughts? I'll <code>CW</code> this just so no one frets.</p> <hr> <p>I still can't lay this to rest. This is what each of the options would look like:</p> <p><strong>Option 1:</strong> (what I prefer)</p> <pre><code>World w; Body b; Fixture f; b.addFixture(f); w.addBody(b); </code></pre> <p><strong>Option 2:</strong> (somewhere in the middle)</p> <pre><code>World w; Body b(w); Fixture f(b); </code></pre> <p><strong>Option 3:</strong> (how Box2D does it)</p> <pre><code>World *w = new World; Body *b = w-&gt;CreateBody(args); Fixture *f = b-&gt;CreateFixture(args); </code></pre> <p>Options 2 and 3 aren't so different, but it changes who has control over is creating the objects.</p> <p>How would I actually implement option 3 though? <code>World::CreateBody()</code> has to call <code>b2World::CreateBody(args)</code> which calls <code>b2Body::b2Body()</code> and returns <code>b2Body</code> but never calls <code>Body::Body(args)</code> which is a problem. The <code>b2Body</code> would get fully initialized, but my wrapper has no place to do it's thing... More specifically, how would I write <code>World::CreateBody(const BodyDef &amp;bd)</code>? Assuming BodyDef inherited from b2BodyDef, Body from b2Body, World from b2World, etc.</p>
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    1. COI think that this is an entirely legitimate design question, no need for CW.
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    2. COOh well... I'm more interested in the answers than the rep... I forgot that answers can't gain rep either. Oops.
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