control_structures_impl.hpp

boost库提供标准的C++ API 配合dev c++使用,功能更加强大

// PHASE 6:2
template<class A, class B>
struct return_type_2_ifthenelsereturn<2, false, false, false, A, B> {
  typedef 
    detail::return_type_deduction_failure<return_type_2_ifthenelsereturn> type;
  // types_do_not_match_in_conditional_expression 
};



// PHASE 5: now we know that types are not arithmetic.
template<class A, class B>
struct non_numeric_types {
  typedef typename 
    return_type_2_ifthenelsereturn<
      1, // phase 1 
      is_convertible<A,B>::value, 
      is_convertible<B,A>::value, 
      is_same<A,B>::value,
      A, 
      B>::type type;
};

// PHASE 4 : 
// the base case covers arithmetic types with differing promote codes
// use the type deduction of arithmetic_actions
template<int CodeA, int CodeB, class A, class B>
struct arithmetic_or_not {
  typedef typename
    return_type_2<arithmetic_action<plus_action>, A, B>::type type; 
  // plus_action is just a random pick, has to be a concrete instance
};

// this case covers the case of artihmetic types with the same promote codes. 
// non numeric deduction is used since e.g. integral promotion is not 
// performed with operator ?: 
template<int CodeA, class A, class B>
struct arithmetic_or_not<CodeA, CodeA, A, B> {
  typedef typename non_numeric_types<A, B>::type type; 
};

// if either A or B has promote code -1 it is not an arithmetic type
template<class A, class B>
struct arithmetic_or_not <-1, -1, A, B> {
  typedef typename non_numeric_types<A, B>::type type;
};
template<int CodeB, class A, class B>
struct arithmetic_or_not <-1, CodeB, A, B> {
  typedef typename non_numeric_types<A, B>::type type;
};
template<int CodeA, class A, class B>
struct arithmetic_or_not <CodeA, -1, A, B> {
  typedef typename non_numeric_types<A, B>::type type;
};




// PHASE 3 : Are the types same?
// No, check if they are arithmetic or not
template <class A, class B>
struct same_or_not {
  typedef typename detail::remove_reference_and_cv<A>::type plainA;
  typedef typename detail::remove_reference_and_cv<B>::type plainB;

  typedef typename 
    arithmetic_or_not<
      detail::promote_code<plainA>::value, 
      detail::promote_code<plainB>::value, 
      A, 
      B>::type type;
};
// Yes, clear.
template <class A> struct same_or_not<A, A> {
  typedef A type;
};

} // detail

// PHASE 2 : Perform first the potential array_to_pointer conversion 
template<class A, class B>
struct return_type_2<other_action<ifthenelsereturn_action>, A, B> { 

  typedef typename detail::array_to_pointer<A>::type A1;
  typedef typename detail::array_to_pointer<B>::type B1;

  typedef typename 
    boost::add_const<typename detail::same_or_not<A1, B1>::type>::type type;
};

// PHASE 1 : Deduction is based on the second and third operand


// return type specialization for conditional expression ends -----------




// Control loop lambda_functor_base specializations.

// Specialization for for_loop.
template<class Args>
class 
lambda_functor_base<forloop_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    for(detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS); 
        detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); 
        detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS))
      
      detail::select(boost::tuples::get<3>(args), CALL_ACTUAL_ARGS);
  }
};

// No body case
template<class Args>
class 
lambda_functor_base<forloop_no_body_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    for(detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS); 
        detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); 
        detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS)) {}
   }
};


// Specialization for while_loop.
template<class Args>
class 
lambda_functor_base<whileloop_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    while(detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS))
      
      detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS);
  }
};

// No body case
template<class Args> 
class 
lambda_functor_base<whileloop_no_body_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
          while(detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) {}
  }
};

// Specialization for do_while_loop.
// Note that the first argument is the condition.
template<class Args>
class 
lambda_functor_base<dowhileloop_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    do {
      detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS);      
    } while (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS) );
  }
};

// No body case
template<class Args>
class 
lambda_functor_base<dowhileloop_no_body_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
          do {} while (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS) );
  }
};


// Specialization for if_then.
template<class Args>
class 
lambda_functor_base<ifthen_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); 
  }
};

// Specialization for if_then_else.
template<class Args>
class 
lambda_functor_base<ifthenelse_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) 
      detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); 
    else 
      detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS);
  }
};

// Specialization of lambda_functor_base for if_then_else_return.
template<class Args>
class 
lambda_functor_base<other_action<ifthenelsereturn_action>, Args> {
public:
  Args args;

  template <class SigArgs> struct sig {
  private:
    typedef typename detail::nth_return_type_sig<1, Args, SigArgs>::type ret1;
    typedef typename detail::nth_return_type_sig<2, Args, SigArgs>::type ret2;
  public:
    typedef typename return_type_2<
      other_action<ifthenelsereturn_action>, ret1, ret2
    >::type type;
  };

public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    return (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) ?
       detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS) 
    : 
       detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS);
  }
};

} // lambda
} // boost

#endif // BOOST_LAMBDA_CONTROL_CONSTRUCTS_HPP