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copied!<p>The question seems to me to be equivalent to,"Why can I use a class as a value?" It's a good question. </p> <p>There are two major things you can do with a class in ActionScript; you can <em>instantiate</em> it, and you can <em>access static properites</em> of it. (Okay, there are other things, but those are the obvious ones.) Instantiating a class is probably the most relevant use of a class as a value; the Class is its own <a href="http://www.c2.com/cgi/wiki?FactoryPattern" rel="nofollow noreferrer" title="Factory Pattern">factory</a>, like ones you would make explicitly in C++ or Java.</p> <p>Here's an example from a small Tetris game I was writing as an exercise. I had two classes, Brick and SceneBrick. A Brick was an in-game brick, the ones that fall and pile up. A SceneBrick was a brick just drawn in as the frame of the play area.</p> <p>However, I used one function to draw both of them, without referring to either type within the function:</p> <pre><code>function drawBricks(xs:Array, ys:Array, brickType:Class){ xs.map(function(o,i,a){ var brick = new brickType(); // etc. }); } </code></pre> <p>And I could use that like this:</p> <pre><code>drawBricks([0,1,2,3], [4,4,4,4], Brick); // draw a long piece drawBricks(times(0, 21), countFrom(0, 21), SceneBrick); // draw a big vertical "wall" </code></pre> <p>In ActionScript, you can pass around a class as a value and use it to instantiate that class. In a language like Java or C++, you would have to either use it as a parameter for a generic class or define factory classes with some common supertype in order to do this.</p>

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