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#include <iostream>
template <typename T>
class Expression
{
const T& expr;
public:
Expression(const T& t2):expr(t2){}
typename T::result operator()()
{
std::cout<<"expr eval"<<std::endl;
expr();
}
};
template <class T> Expression<T> makeExpression(const T& t)
{
std::cout<<"make expr"<<std::endl;
return Expression<T>(t);
}
template <class T> class Var
{
T t;
public :
Var(const Var& o):t(o.t){std::cout<<"copy"<<std::endl;}
Var(T t2):t(t2){std::cout<<"value "<<t<<std::endl;}
Var():t(T()){}
Var(Var&& o):t(std::move(o.t)){std::cout<<"move"<<std::endl;}
T operator()() const
{
return t;
}
Var& operator=(T o)
{
t=o;
return *this;
}
~Var(){std::cout<<"dst"<<std::endl;}
typedef T result;
};
template <typename T,typename U,typename Op> class ExpressionBin
{
const T& t;
const U& u;
Op op;
public:
ExpressionBin(){std::cout<<"wtf"<<std::endl;} // <<LA
ExpressionBin(const T& tt,const U& uu):
t(tt),
u(uu),op(Op())
{
}
typedef decltype(op(T(),U())) result;
result operator()() const
{
return op(t,u);
}
};
#define helperEval(op) template <class T, class U> \
decltype((typename T::result() op typename U::result())) \
operator()(const T& t,const U& u) const \
{ \
std::cout<<#op " called " \
<<t()<<" "<<u()<<std::endl; \
return t() op u(); \
}
struct plus
{
helperEval(+)
};
struct mul
{
helperEval(*)
};
struct DIV
{
helperEval(/)
};
struct moins
{
helperEval(-)
};
template <class T, class U> ExpressionBin<T,U,plus>
operator+(const T& t,const U& u)
{
return ExpressionBin<T,U,plus>(t,u);
}
template <class T, class U> ExpressionBin<T,U,mul>
operator*(const T& t,const U& u)
{
return ExpressionBin<T,U,mul>(t,u);
}
template <class T, class U> ExpressionBin<T,U,DIV>
operator/(const T& t,const U& u)
{
return ExpressionBin<T,U,DIV>(t,u);
}
template <class T, class U> ExpressionBin<T,U,moins>
operator-(const T& t,const U& u)
{
return ExpressionBin<T,U,moins>(t,u);
}
int main(int argc, char *argv[])
{
Var<int> x(5);
const Var<int> y(3);
const Var<double> z(+2.5);
Var<double> a;
Var<int> b=2;
auto e= makeExpression(x*y+z);
std::cout<<"========="<<std::endl;
a=0.5;
std::cout<<"=>"<<e()<<std::endl;
std::cout<<"========="<<std::endl;
return 0;
} |
