C++ Expression Templates

Listing 3: Source code for template-based solution

class Literal {
public:
   Literal(const double v) : _val(v) {}
   double eval() const { return _val; }
private:
   const double _val;
};

class Variable {
public:
   Variable(double& v) : _val(v) {}
   double eval() const { return _val; }
private:
   double& _val;
};


template <class ExprT1,class ExprT2, class BinOp>
class BinaryExpr {
public:
   BinaryExpr(ExprT1 e1, ExprT2 e2,BinOp op=BinOp())
      : _expr1(e1),_expr2(e2),_op(op) {}
   double eval() const 
   { return _op(_expr1.eval(),_expr2.eval()); }
private:
   ExprT1 _expr1;
   ExprT2 _expr2;
   BinOp  _op;
};

...
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