multiple-inheritance

问题 I have two distinct (no inheritance) interfaces: IInvestable and IPricable and two classes: IndexClass and FundClass that are stored in seperate tables in my DB. IndexClass is IPriceable FundClass is IPriceable and IInvestable . I need a table to store prices against an IndexClass and a FundClass I need a table to store that FundClasses are invested in. One way might be to have two tables: Pricable and Investable which just have an ID column. Then have a foreign key on IndexClass : PricableID

问题 I have this code, but it does not compile: #include <iostream> #include <stdexcept> #include <cassert> template< class > struct id{}; template< class U, class V> struct base: public id<U>, public id<V> { static const bool value = true; }; template< class U, class V> struct is_different { typedef char (&true_)[1]; typedef char (&false_)[2]; template< class T, class K, bool = base<T,K>::value > struct checker; template< class T, class K> static true_ test( checker<T,K>* ); template< class ,

问题 I have a system of Models: abstract class R00_Model_iUnique { } abstract class R00_Model_iFamilyUnique extends R00_Model_iUnique { } // for models with hierarchy abstract class R00_Model_iTaggedUnique extends R00_Model_iUnique { } // for models with tags // and, for example class R00_Model_User extends R00_Model_iUnique { } class R00_Model_Comment extends R00_Model_iFamilyUnique { } class R00_Model_Post extends R00_Model_iTaggedUnique { } There is gonna be R00_Model_iCommentableUnique and R00

问题 Aim To implement a proper and efficient view architecture for my project (with maximum reuse of repeated units) About my project My project involves classes taken by tutors and packs published by tutors. No framework has been used but object orientation and class hierarchies are present for model, controller part. I have the following modules - Search->Class listings - list of classes displayed in search results. Student room->Class listings - List of classes a student has purchased Search-

问题 Given the following code class T { public: virtual ~T () {} virtual void foo () = 0; }; class U { public: U() {} ~U() {} void bar () { std::cout << "bar" << std::endl; } }; class A : public U, public T { public: void foo () { std::cout << "foo" << std::endl; } }; int main () { A * a = new A; std::vector<U*> u; std::vector<T*> t; u.push_back(a); t.push_back(reinterpret_cast<T*>(u[0])); u[0]->bar (); t[0]->foo (); delete a; return 0; } I get the output I would expect bar foo However, if I

问题 I have a few function objects that have no member variables. The function objects are very simple in nature. They all inherit from unary_function<> or binary_function<> . For example, a couple of the function objects may be something like this: struct key_to_hash_method_1 : public binary_function<int, int, int> { int operator() (int a, int b) const { /* do something */ } }; template <typename key_to_hash_method> struct hash_shrink_method_1 : public binary_function<int, int, int>, public key

问题 Is it possible to inherit identically named operator which only differ in return type, from two different abstract classes. If so, them: what is the syntax for implementing operators what is the syntax for using/resolving operators what is the overhead in general case, same as for any other virtual function? if you can provide me with a reference or sample code that would be helpful thanks 12struct abstract_matrix { 13 virtual double& operator()(int i, int j); 14}; 15 16 struct abstract_block

问题 I have an e-shop with multiple product types. And i would have thought of the following structure Cart_Item -- Cart_Product -- Cart_Download Order_Item extends Cart_Item -- Order_Product -- Order_Download The problem is that i want to have Order_Product extend Order_Item and Cart_Product. This is because it needs method generic to Order_Item ( get price from Order not from product ) but also methods from Cart_Product ( shipping calculations ) I know that php doesn't support multiple

问题 I have a base class called animal, and a dog and a cat that inherit from Animal. And a multiinheritance class called dogcat, that inherit from dog and cat, in Animal i have method called sleep. When i want to use that method from dogcat, i get the error "DogCat::sleep" is ambiguous, i do understand the problem, but i read in a book that it should be possible, when you declare sleep as virtual - but it does not work. Is this not possible is the book wrong or is there any workaround? class

问题 Assume I have a class implementing two or more COM interfaces (exactly as here): class CMyClass : public IInterface1, public IInterface2 { }; QueryInterface() must return the same pointer for each request of the same interface (it needs an explicit upcast for proper pointer adjustment): if( iid == __uuidof( IUnknown ) ) { *ppv = static_cast<IInterface1*>( this ); //call Addref(), return S_OK } else if( iid == __uuidof( IInterface1 ) ) { *ppv = static_cast<IInterface1*>( this ); //call Addref(