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POWhy can C++ functors be preferable to objects with named methods?
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  1. POWhy can C++ functors be preferable to objects with named methods?
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    copied!<p>I recently have got excited by functors and been using them all over the place. Then the situation arose where I needed my functor to perform two different operations and I thought about adding another method to my functor (not overloading the () operator). Whether this is bad practice or not I am not sure (perhaps you could tell me), but it got me thinking about why I am using functors in the first place and not just objects. So my question is:</p> <p><strong>Is there anything special about overloading the () operator or is it just very slightly more syntactically appealing than using normal named methods?</strong> </p> <p><strong>Update:</strong></p> <p>Firstly, I know why functors may be preferable to function pointers as explained in other questions. I want to know why they can be preferable to objects with named methods.</p> <p>Secondly, as for an example of when I wanted to use another possibly named method of my functor: Basically I have two functions, one which calculates something called the modularity of a graph partition - <code>compute_modularity()</code>, and another which computes the gain in modularity after some change of the partition<code>compute_modularity_gain()</code>. I thought I could pass these functions as part of the same functor into an optimisation algorithm, with the gain as a named function. The reason I don't just pass two functors into the algorithm, is that I want to enforce that <code>compute_modularity_gain()</code> is used only in conjuction with <code>compute_modularity()</code> and not another functor e.g. <code>compute_stability()</code> (which should only be used with <code>compute_stability_gain()</code>. In other words, the gain function must be tightly coupled with its sibling function. If there is another way I can enforce this constraint then please let me know.</p>
 

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