C++實現的一個可以寫遞迴lambda的Y函數_C 語言

最近學習C++11的variadic template argument，終於可以擺脫用fpmacro模板來複製一大堆代碼的做法了，好開心。這個例子的main函數用lambda寫了一個斐波那契數列的遞迴計算函數。跟以往不同的是，在Y函數的協助下，這個lambda表達是可以成功看到自己，然後遞迴調用。當然這仍然需要用普通的C++遞迴來實現，並不是λ-calculus那個高大上的Y Combinator。

#include <functional>#include <memory>#include <iostream>#include <string>using namespace std;template<typename TResult, typename ...TArgs>class YBuilder{private:  function<TResult(function<TResult(TArgs...)>, TArgs...)> partialLambda;public:  YBuilder(function<TResult(function<TResult(TArgs...)>, TArgs...)> _partialLambda)    :partialLambda(_partialLambda)  {  }  TResult operator()(TArgs ...args)const  {    return partialLambda(      [this](TArgs ...args)      {        return this->operator()(args...);      }, args...);  }};template<typename TMethod>struct PartialLambdaTypeRetriver{  typedef void FunctionType;  typedef void LambdaType;  typedef void YBuilderType;};template<typename TClass, typename TResult, typename ...TArgs>struct PartialLambdaTypeRetriver<TResult(__thiscall TClass::*)(function<TResult(TArgs...)>, TArgs...)>{  typedef TResult FunctionType(TArgs...);  typedef TResult LambdaType(function<TResult(TArgs...)>, TArgs...);  typedef YBuilder<TResult, TArgs...> YBuilderType;};template<typename TClass, typename TResult, typename ...TArgs>struct PartialLambdaTypeRetriver<TResult(__thiscall TClass::*)(function<TResult(TArgs...)>, TArgs...)const>{  typedef TResult FunctionType(TArgs...);  typedef TResult LambdaType(function<TResult(TArgs...)>, TArgs...);  typedef YBuilder<TResult, TArgs...> YBuilderType;}; template<typename TLambda>function<typename PartialLambdaTypeRetriver<decltype(&TLambda::operator())>::FunctionType> Y(TLambda partialLambda){  return typename PartialLambdaTypeRetriver<decltype(&TLambda::operator())>::YBuilderType(partialLambda);} int _tmain(int argc, _TCHAR* argv[]){  auto fib = Y([](function<int(int)> self, int index)  {    return index<2      ?1      :self(index-1)+self(index-2);  });   for (int i = 0; i < 10; i++)  {    cout << fib(i) << " ";  }  cout << endl;}