Expression.h

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#ifndef PhysicsTools_Utilities_Expression_h
#define PhysicsTools_Utilities_Expression_h
#include "PhysicsTools/Utilities/interface/FunctionsIO.h"
#include <ostream>
#include <memory>

namespace funct {

  struct AbsExpression {
    virtual ~AbsExpression() {}
    virtual double operator()() const = 0;
    virtual AbsExpression* clone() const = 0;
    virtual std::ostream& print(std::ostream& cout) const = 0;
  };

  template <typename F>
  struct ExpressionT : public AbsExpression {
    inline ExpressionT(const F& f) : _f(f) {}
    ~ExpressionT() override {}
    double operator()() const override { return _f(); }
    AbsExpression* clone() const override { return new ExpressionT<F>(_f); }
    std::ostream& print(std::ostream& cout) const override { return cout << _f; }

  private:
    F _f;
  };

  struct Expression {
    inline Expression() {}
    template <typename F>
    inline Expression(const F& f) : _f(new ExpressionT<F>(f)) {}
    inline Expression(const Expression& e) : _f(e._f->clone()) {}
    inline Expression& operator=(const Expression& e) {
      _f.reset(e._f->clone());
      return *this;
    }
    inline double operator()() const { return (*_f)(); }
    inline std::ostream& print(std::ostream& cout) const { return _f->print(cout); }

  private:
    std::unique_ptr<AbsExpression> _f;
  };

  inline std::ostream& operator<<(std::ostream& cout, const Expression& e) {
    e.print(cout);
    return cout;
  }

  struct AbsFunctExpression {
    virtual ~AbsFunctExpression() {}
    virtual double operator()(double x) const = 0;
    virtual AbsFunctExpression* clone() const = 0;
  };

  template <typename F>
  struct FunctExpressionT : public AbsFunctExpression {
    inline FunctExpressionT(const F& f) : _f(f) {}
    ~FunctExpressionT() override {}
    double operator()(double x) const override { return _f(x); }
    AbsFunctExpression* clone() const override { return new FunctExpressionT<F>(_f); }

  private:
    F _f;
  };

  struct FunctExpression {
    inline FunctExpression() {}
    template <typename F>
    inline FunctExpression(const F& f) : _f(new FunctExpressionT<F>(f)) {}
    inline FunctExpression(const FunctExpression& e) : _f(e._f->clone()) {}
    inline FunctExpression& operator=(const FunctExpression& e) {
      _f.reset(e._f->clone());
      return *this;
    }
    inline double operator()(double x) const { return (*_f)(x); }

  private:
    std::unique_ptr<AbsFunctExpression> _f;
  };

}  // namespace funct

#endif