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POC++ Templates. Can't use inherited function
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2013-09-13T00:54:10.057
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2017-10-23T18:51:34.563
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2017-10-23T18:51:34.563
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Well this has been giving me grief... <pre><code>#include <iostream> class InterfaceClass { public: void test() { std::cout<<"Hello there.\n"; } }; template <class T> class TemplateClass { public: T t; }; class TestClass: public InterfaceClass {}; class TestInheritor { public: TemplateClass < InterfaceClass >* templateInherit; InterfaceClass* normalInherit; void test() { normalInherit->test(); templateInherit->t.test(); } }; int main (int nargs, char ** arg) { TestInheritor ti; ti.normalInherit = new TestClass; // THIS ONE COMPILES OKAY. //ti.templateInherit = new TemplateClass <TestClass>; // COMPILE ERROR. // THIS WORKS THOUGH TemplateClass <TestClass> * tempClass = new TemplateClass <TestClass>; ti.templateInherit=(TemplateClass <InterfaceClass>*)tempClass; // WHY DO I HAVE TO EXPLICITLY CAST? // OUTPUT WORKS AS EXPECTED. ti.test(); return 0; } </code></pre> The normal inheritance example works just fine. The TestClass is automatically converted to a InterfaceClass. However, with the template example, it gives a compile error: <pre><code>error: cannot convert 'TemplateClass<TestClass>*' to 'TemplateClass<InterfaceClass>*' in assignment </code></pre> In my mind, it is obvious that you can convert <code>TemplateClass<TestClass>*</code> to <code>TemplateClass<InterfaceClass>*</code>... So what am I missing here? I can fix it by explicitly casting the template class to the base class, I am able to use the inherited test() function without any problem... So why am I required to explicitly cast the template class? Sorry if that's confusing... It's hard for me to explain this problem. <hr> Okay, I understand the issue a little more. I have decided to add a template to TestInheritor like so: <pre><code>template <class T2> class TestInheritor { public: TemplateClass < T2 >* templateInherit; InterfaceClass* normalInherit; void test() { normalInherit->test(); templateInherit->t.test(); } }; int main (int nargs, char ** arg) { TestInheritor <TestClass> ti; ti.normalInherit = new TestClass; ti.templateInherit = new TemplateClass <TestClass>; ti.test(); return 0; } </code></pre> Probably not the perfect solution, but it works for my purposes. <hr> Ah, and I see your solution: <pre><code>#include <iostream> class InterfaceClass { public: void test() { std::cout<<"Hello there.\n"; } }; class TestClass: public InterfaceClass {}; template <class T> class TemplateClass { public: T t; }; template<> class TemplateClass<TestClass> : public TemplateClass<InterfaceClass> { public: }; class TestInheritor { public: TemplateClass < InterfaceClass >* templateInherit; InterfaceClass* normalInherit; void test() { normalInherit->test(); templateInherit->t.test(); } }; int main (int nargs, char ** arg) { TestInheritor ti; ti.normalInherit = new TestClass; ti.templateInherit = new TemplateClass <TestClass>; ti.test(); return 0; } </code></pre>
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<c++><templates><inheritance><casting><explicit>
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C++ Templates. Can't use inherited function
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