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POWhen classes want to couple
 

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    <p>I am having an issue with 2 classes that were once nicely separated, but now they want to couple.</p> <p>Without getting too much into the specifics of the problem, here it is:</p> <p>I used to have a class Triangle that contained 3 space-position vertices.</p> <pre><code>class Triangle { Vertex a,b,c ; // vertices a, b and c } ; </code></pre> <p>There were many Triangle instances in the program, so each had retained their own copy of their vertices. Member functions such as <code>getArea()</code>, <code>getCentroid()</code> etc were written in class <code>Triangle</code>, and since each <code>Triangle</code> instance had copies of Vertex a, b and c, finding the area or centroid had no dependence on other classes. As it should be!</p> <p>Then I wanted to move to a vertex-array/index buffer style representation, for other reasons. This means all vertices are stored in a single array located in a <code>Scene</code> object, and each <code>Triangle</code> retains only REFERENCES to the vertices in <code>Scene</code>, not copies of the vertices themselves. At first, I tried switching out for pointers:</p> <pre><code>class Scene { std::vector&lt;Vertex&gt; masterVertexList ; } ; class Triangle { Vertex *a,*b,*c ; // vertices a, b and c are pointers // into the Scene object's master vertex list } ; </code></pre> <p>(In case you're wondering about the benefits, I did it for reasons mostly to do with triangles that share vertices. If *a moves then all triangles that use that vertex are updated automatically).</p> <p>This would have been a really good solution! But it didn't work reliably, <a href="https://stackoverflow.com/questions/3287801/pointers-to-elements-of-stdvector-and-stdlist">because std::vector invalidates pointers</a>, and I was using a std::vector for the master vertex list in class <code>Scene</code>.</p> <p>So I had to use integers:</p> <pre><code>class Triangle { int a,b,c ; // integer index values // into the Scene object's master vertex list } ; </code></pre> <p>But now I have this new coupling problem: to find its own area or centroid, class <code>Triangle</code> needs access to <code>class Scene</code> where before it did not. It seems like I've fsck`d something up, but not really.</p> <p>WWYD?</p>
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    1. COHow is this language agnostic?
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      1. USNathan Osman
    2. COChanged to C++.
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    3. COThese classes remind me of George Costanza: "I've coupled! I've coupled!"
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      1. USFrederick The Fool
 

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