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#include <iostream>
#include <vector>
#include <functional>
// See also addis.cc
using namespace std;
enum
{
ADD,
SUB,
MUL
};
template<typename LHS, typename RHS, int operation>
struct BinExpr
{
template<typename Type>
struct BasicType;
template<typename LH, typename RH, int oper>
struct BasicType<BinExpr<LH, RH, oper>>;
typedef typename BasicType<RHS>::ObjType ObjType;
typedef typename ObjType::value_type value_type;
LHS const &d_lhs;
RHS const &d_rhs;
BinExpr(LHS const &lhs, RHS const &rhs)
:
d_lhs(lhs),
d_rhs(rhs)
{}
size_t size() const
{
return d_lhs.size();
}
template <typename LH, typename RH, int oper>
struct Operation;
value_type operator[](size_t ix) const
{
return Operation<LHS, RHS, operation>::cpt(d_lhs[ix], d_rhs[ix]);
// *************** this causes
// calling
// the proper
// cpt ****************
}
operator ObjType() const
{
ObjType retVal;
retVal.reserve(size());
for (size_t ix = 0, end = size(); ix != end; ++ix)
new(&retVal[ix]) value_type{ (*this)[ix] };
return retVal;
}
};
template<typename LHS, typename RHS, int operation>
template<typename Type>
struct BinExpr<LHS, RHS, operation>::BasicType
{
typedef Type ObjType;
};
template<typename LHS, typename RHS, int operation>
template<typename LH, typename RH, int oper>
struct BinExpr<LHS, RHS, operation>::BasicType<BinExpr<LH, RH, oper>>
{
typedef typename BinExpr<LH, RH, oper>::ObjType ObjType;
};
template<typename LHS, typename RHS, int operation>
template <typename LH, typename RH>
struct BinExpr<LHS, RHS, operation>::Operation<LH, RH, ADD>
{
static value_type cpt(value_type const &lhs, value_type const &rhs)
{
return lhs + rhs;
};
};
template<typename LHS, typename RHS, int operation>
template <typename LH, typename RH>
struct BinExpr<LHS, RHS, operation>::Operation<LH, RH, SUB>
{
static value_type cpt(value_type const &lhs, value_type const &rhs)
{
return lhs - rhs;
};
};
template<typename LHS, typename RHS>
BinExpr<LHS, RHS, ADD> operator+(LHS const &lhs, RHS const &rhs)
{
return BinExpr<LHS, RHS, ADD>(lhs, rhs);
}
template<typename LHS, typename RHS>
BinExpr<LHS, RHS, SUB> operator-(LHS const &lhs, RHS const &rhs)
{
return BinExpr<LHS, RHS, SUB>(lhs, rhs);
}
struct VI // define the data structure to
{ // operate on
static size_t s_count;
typedef int value_type;
VI() = default;
VI(VI const &other)
{
(*this)[0] = other[0];
cout << "CC, count = " << s_count << '\n';
}
VI(VI &&tmp)
{
(*this)[0] = tmp[0];
cout << "MC, count = " << s_count << '\n';
}
int d_value = 0;
size_t size() const
{
return 1;
};
void reserve(size_t count)
{};
int &operator[](size_t idx)
{
++s_count;
return d_value;
}
int const &operator[](size_t idx) const
{
++s_count;
return d_value;
}
};
size_t VI::s_count;
int main()
{
VI a, b, c, d;
VI e = a + b + c + d;
// (a + b + c + d).operator VI(); // the resulting sum is computed once
// the conversion operator is called.
// static_cast<VI>(a + b + c + d);
cout << "# index computations: " << VI::s_count << '\n';
}
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