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A class that **loosely enforces** both static and non-static member function implementation. See comments for more.
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| #include <iostream> | |
| #include <iomanip> | |
| #include "assert.h" | |
| //Forward declare templated class | |
| template<typename T> class TestingStuff; | |
| //Templated superclass | |
| template<typename T> | |
| class TestingStuff { | |
| private: | |
| //Reference to templated base | |
| static TestingStuff<T>* reference; | |
| public: | |
| //Dummy non-static member variable | |
| double i = 3.1415926535897932384626433826795; | |
| //public static constant static non-member function pointer | |
| static constexpr void (*staticFuncRef)() = &T::doNothing; | |
| //public static constant non-static sub-member function pointer | |
| static constexpr void (T::*funcRef)() = &T::nonStaticDoNothing; | |
| TestingStuff() { | |
| /* initialize state or put public constructer into private block to enforce | |
| * singleton instances, only accessible through TestingStuff<T>#getInstance | |
| */ | |
| } | |
| //Public static singleton fetching function | |
| static TestingStuff<T>* getInstance() { | |
| return reference ? ({assert(reference); reference;}) : (reference = new TestingStuff<T>()); | |
| } | |
| //Member function (can modify state) | |
| void nonStaticDoNothing(); | |
| //Static non-member friend function (can modify state) | |
| friend void doNothing(); | |
| }; | |
| //Declare singleton TestingStuff<T>* variable so it can be assigned | |
| template<typename T> TestingStuff<T>* TestingStuff<T>::reference; | |
| //Struct example | |
| struct TestStruct { | |
| void nonStaticDoNothing() {} | |
| //Static non-member function with access to member variables of 'TestStructAlias' | |
| static void doNothing() { | |
| std::cout << std::setprecision(53) << TestingStuff<TestStruct>::getInstance()->i << std::endl; | |
| } | |
| }; | |
| //Simple type alias for convenience | |
| typedef TestingStuff<TestStruct> TSTS; | |
| //Class example | |
| class SubClass : TestingStuff<SubClass> { | |
| public: | |
| void nonStaticDoNothing() { | |
| std::cout << "Did nothing!" << std::endl; | |
| } | |
| static void doNothing() { | |
| std::cout << "Did a static nothing!" << std::endl; | |
| } | |
| }; | |
| //Simple type alias for convenience | |
| typedef TestingStuff<SubClass> TFSC; | |
| int main() { | |
| //Struct inheritance | |
| TestStruct ts; | |
| //Considered bad practice to invoke static members like non-static members | |
| ts.doNothing(); // or TestStruct::doNothing(); or TSTS::staticFuncRef(); | |
| ts.nonStaticDoNothing(); // or (ts->*TSTS::funcRef)(); | |
| //Class inheritance | |
| SubClass* sc = new SubClass(); | |
| TFSC::staticFuncRef(); // or SubClass::doNothing(); | |
| (sc->*TFSC::funcRef)(); // or sc->nonStaticDoNothing(); | |
| } |
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A class that loosely enforces both static and non-static member function implementation. Why loosely? Simple: the
constexprstatements in the public block of theTestingStuffclass cannot enforce function implementation, in the template typeT, unless they are invoked (in which case, you'll get a compiler error if you're missing a function). To strictly enforce member implementation, simply move the function pointer assignments into the constructor of theTestingStuffclass. (Note: as a consequence of doing this, you'll also have to change the pointers over toconsts, as they will no longer be qualifiedconstexprstatements.)