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POHow to invoke non-default constructor for template class?
 

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  1. POHow to invoke non-default constructor for template class?
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    <p>I have the following code structure (<code>Resource</code> and <code>Parameter</code> are empty classes):</p> <p>Solver.cpp</p> <pre><code>#include "Solver.h" #include "ValueFunction.h" using namespace std; template&lt;typename T&gt; Solver&lt;T&gt;::Solver(vector&lt;vector&lt;Resource&gt; &gt;&amp; resources, const Parameter&amp; params) : states(resources.size()) { for (int i=0; i&lt;resources.size(); i++) { states[i] = State&lt;T&gt;(resources[i], params); } } // Explicit class declaration template class Solver&lt;ValueFunction&gt;; </code></pre> <p>Solver.h</p> <pre><code>#ifndef SOLVER_H_ #define SOLVER_H_ #include &lt;vector&gt; #include "Resource.h" #include "Parameter.h" #include "State.h" template&lt;typename T&gt; class Solver { public: Solver( std::vector&lt;std::vector&lt;Resource&gt; &gt;&amp; resources, const Parameter&amp; params ); private: std::vector&lt;State&lt;T&gt; &gt; states; }; #endif /* SOLVER_H_ */ </code></pre> <p>State.cpp</p> <pre><code>#include "State.h" #include "ValueFunction.h" using namespace std; template&lt;typename T&gt; State&lt;T&gt;::State(vector&lt;Resource&gt;&amp; _resources, const Parameter&amp; params) : resources(_resources), valfuncs(_resources.size(), T(params)) { } template class State&lt;ValueFunction&gt;; </code></pre> <p>State.h</p> <pre><code>#ifndef STATE_H_ #define STATE_H_ #include &lt;vector&gt; #include "Parameter.h" #include "Resource.h" template&lt;typename T&gt; class State { public: State() {}; State(std::vector&lt;Resource&gt;&amp; _resources, const Parameter&amp; params); ~State() {}; private: std::vector&lt;Resource&gt; resources; std::vector&lt;T&gt; valfuncs; }; #endif /* STATE_H_ */ </code></pre> <p>ValueFunction.cpp</p> <pre><code>#include "ValueFunction.h" ValueFunction::ValueFunction(const Parameter&amp; _params) : params(_params) { } </code></pre> <p>ValueFunction.h</p> <pre><code>#ifndef VALUEFUNCTION_H_ #define VALUEFUNCTION_H_ #include "Parameter.h" class ValueFunction { public: ValueFunction(const Parameter&amp; _params); private: const Parameter&amp; params; }; #endif /* VALUEFUNCTION_H_ */ </code></pre> <p>With the following call:</p> <pre><code>#include "Solver.h" #include "State.h" #include "ValueFunction.h" #include "Parameter.h" using namespace std; int main(int argc, char *argv[]) { Parameter params; vector&lt;vector&lt;Resource&gt; &gt; resources(4); Solver&lt;ValueFunction&gt; sol(resources, params); return 0; } </code></pre> <p>And I get the following error:</p> <pre><code>Solver.cpp:18:16: instantiated from here ValueFunction.h:6:21: error: non-static reference member ‘const Parameter&amp; ValueFunction::params’, can't use default assignment operator </code></pre> <p>How can I invoke the non-default constructor for <code>ValueFunction</code> correctly, or is there an other way to initialize an <code>std::vector</code> with a non-default constructor (passing a constant reference)?</p> <p><strong>Update</strong></p> <p>The error is explained in this <a href="https://stackoverflow.com/questions/634662/non-static-const-member-cant-use-default-assignment-operator">post</a>. But the workaround for my problem is not entirly clear. Any suggestions?</p>
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    1. USReza
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      1. POHow to invoke non-default constructor for template class?
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    1. COThe error occurs because I want to initialize `params` with `_params` in the class `ValueFunction` (No idea why this causes an error).
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      1. POHow to invoke non-default constructor for template class?
      1. USReza
    2. COYou'll have to put the definitions of the template class in the header files. Template definitions need to be visible at the point of instantiation. In your case they're not, so your compiler is confused. See [this question](http://stackoverflow.com/questions/3749099/why-should-the-implementation-and-the-declaration-of-a-template-class-be-in-the). I threw your code together in one source file and it compiles.
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      1. POHow to invoke non-default constructor for template class?
      1. USjrok
    3. CO@jrok it is not a instatiation problem, as far as I know the implicit instantiation is as accepted by the compiler as the explicite (see [here](http://www.cplusplus.com/forum/articles/14272/)).
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