CRTP. Double static polymorphism

double_static_polymorphism.cpp

//
// CRTP. Double static polymorphism
//
// g++ -std=c++14 1.cpp && ./a.out

#include <iostream>
#include <string>


using std::cout;
using std::endl;
using std::string;

// CT interface WordGetterBase
template<typename derived_t>
struct WordGetterBase
{
    string getWord() const {
        return static_cast<const derived_t*>(this)->getWord();
    }
    void printWord() const {
        cout << getWord() << endl;
    }
};


// Implemmentations WordGetterBase
struct WordGetterW1: public WordGetterBase<WordGetterW1>
{
    string getWord() const {
        return "Str1";
    }
};
struct WordGetterW2: public WordGetterBase<WordGetterW2>
{
    string getWord() const {
        return "Str2";
    }
};

//
// CT interface StrPrinterBase
//
template <template <typename WordGetter> class derived_t, typename WordGetter>
struct StrPrinterBase: public WordGetter
{
    string getWord() const {
        return static_cast<const WordGetter*>(this)->getWord();
    }

    void printStr() const {
        //static_cast<const WordGetter* >(this)->printWord();
        return static_cast< derived_t<WordGetter>* >(this)->printStr();
    }
};

// Implemmentations StrPrinterBase
template <class WordGetter>
struct StrPrinter1: public StrPrinterBase<StrPrinter1, WordGetter>
{
   using base =  StrPrinterBase<StrPrinter1, WordGetter>; 
    void printStr() const {
        cout << "[ " << base::getWord() << " ]" << endl;
    }
};
template <class WordGetter>
struct StrPrinter2: public StrPrinterBase<StrPrinter1, WordGetter>
{
   using base =  StrPrinterBase<StrPrinter1, WordGetter>; 
    void printStr() const {
        cout << "{ " << base::getWord() << " }" << endl;
    }
};



int main()
{
    WordGetterW1{}.printWord();
    WordGetterW2{}.printWord();

    cout << "~~~~~~~~~~~~" << endl;

    StrPrinter1<WordGetterW1>{}.printStr();
    StrPrinter2<WordGetterW2>{}.printStr();
    StrPrinter2<WordGetterW1>{}.printStr();

    //output:
    //Str1
    //Str2
    //~~~~~~~~~~~~
    //[ Str1 ]
    //{ Str2 }
    //{ Str1 }


    return 0;
}