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POUsing std::function with union in C++11
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  1. POUsing std::function with union in C++11
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    copied!<p>I am trying to define a class that has functions with different numbers of parameters stored in a union. The class is initialized with a function object and necessary parameters. I am getting these compiler errors at the locations marked (1) and (2)</p> <p>(1) Destructor of '_' is implicitly deleted because variant field 'f_V' has a non-trivial destructor</p> <p>(2) Destructor of 'MyClass' is implicitly deleted because field 'functions' has a deleted destructor</p> <p>I simply want to declare a union of different function objects, and depending on the parameters passed-in be able to pick the appropriate function and call it. Why am I getting these errors and how should I rewrite this code?</p> <pre><code>template&lt;typename VARIABLE&gt; struct MyClass { MyClass(VARIABLE *p, const std::function&lt;void (VARIABLE&amp;)&gt;&amp; f) { functions.f_V = f; ... } protected: union _ { std::function&lt;void (VARIABLE &amp;)&gt; f_V; // (1) std::function&lt;void (const VARIABLE &amp;, VARIABLE &amp;)&gt; f_vV; std::function&lt;void (const VARIABLE &amp;, const VARIABLE &amp;, VARIABLE &amp;)&gt; f_vvV; std::function&lt;void (const VARIABLE &amp;, const VARIABLE &amp;, const VARIABLE &amp;, VARIABLE &amp;)&gt; f_vvvV; } functions; // (2) ... }; </code></pre> <p>EDIT: I am trying to accomplish storage of lambda functions having variable argument lists in a container. Something like this:</p> <pre><code>std::vector&lt;MyClass&lt;MyVariable&gt;&gt; myContainerOfLambdas; MyVariable A,B,TO; auto lambda1 = [this](const MyVariable&amp; a, MyVariable&amp; to) { ... }; myContainerOfLambdas.push_back(MyClass&lt;MyVariable&gt;(A,TO,lambda1)); auto lambda2 = [this](const MyVariable&amp; a, const MyVariable&amp; b, MyVariable&amp; to) { ... }; myContainerOfLambdas.push_back(MyClass&lt;MyVariable&gt;(A,B,TO,lambda2)); ... // iterate over the stored MyClass objects holding the lamda functions and the parameters // to call them for(MyClass&lt;MyVariable&gt; &amp; e:myContainerOfLambdas) { e(); // here the appropriate lambda function will be invoked with the appropriate values // stored in MyClass } </code></pre> <p>NOTE: For brevity I have omitted the definition of the () operator in MyClass, but it simply calls the right function object with the right parameters.</p> <p>If you see a better design approach to this, fine, please direct me in the right direction. Thanks!</p>
 

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