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POSome troubles with C++ template pointer-to-member based property realization
 

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  1. POSome troubles with C++ template pointer-to-member based property realization
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    <p>My target was to make properties in C++ like in C# - with non-trivial set/get behavior. Here, object of Property holds refs to master of the prop and its set/get methods.</p> <p>Realisation, content of Property.h:</p> <pre><code>#include &lt;iostream&gt; using namespace std; namespace First { template &lt;class Master, class Type&gt; struct Property { Master &amp;master; const Type (Master::*&amp;get) () const; Type (Master::*&amp;set)(Type value); Property ( Master &amp;master, const Type (Master::*get) () const, Type (Master::*set)(Type value) ): get(get), set(set), master(master) { } operator const Type() const { cout &lt;&lt; "inside" &lt;&lt; endl; return (master.*get)(); } Type operator = (Type value) { return (master.*set)(value); } }; // Test chamber. class R { float x; const float getx() const { cout &lt;&lt; "returning " &lt;&lt; 0 &lt;&lt; endl; return 0; } float setx(float value) { cout &lt;&lt; "setting " &lt;&lt; value &lt;&lt; " in place of " &lt;&lt; x &lt;&lt; endl; return x = value; } public: Property&lt;R, float&gt; X; R(): X(*this, &amp;R::getx, &amp;R::setx) { } }; } </code></pre> <p>I also created .cpp file:</p> <pre><code>#include "Property.h" using namespace First; int main() { R r; r.X = 10; float y = r.X; } </code></pre> <p>The program makes "assign" step, printing 'setting 0 to 10', but segfaults on call to "retrieve" step, no difference what code (or no at all) inside 'R::getx()'.</p> <pre><code>~/Sources$ ./a.out setting 10 in place of 0 inside zsh: segmentation fault ./a.out </code></pre> <p>It seems that call to (master.*get()) itself causes a failure. What is wrong in this code?</p> <p>UPD: A tested out that any other call to master's functions leads to segfault, only one call of (master.*set) successes. Seems that this call invalidates state of object, member-to-ptr, Property itself or Moon phase.</p>
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    1. USZeroArcan
    1. USZeroArcan
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    1. COYou've already been given the correct answer. I would also suggest that you make your `Property::master` a pointer rather than a reference, otherwise `Property` is non-copyable as would be any class using it.
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      1. POSome troubles with C++ template pointer-to-member based property realization
      1. USNicola Musatti
    2. CO@ZeroArcan: No. The call to `(master.*set)(value)` is also a problem. Its just that you don't get to see the problem, unluckily.
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      1. POSome troubles with C++ template pointer-to-member based property realization
      1. USNawaz
    3. CO@Nicola: it wont be copyable whenever master is ref or pointer - I should override copy ctor of containing object to get valid effect.
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      1. POSome troubles with C++ template pointer-to-member based property realization
      1. USZeroArcan
 

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