exceptions.hpp

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// -- Boost Lambda Library -- exceptions.hpp ----------------
//
// Copyright (C) 2000 Gary Powell ([e-mail])
// Copyright (C) 1999, 2000 Jaakko J鋜vi ([e-mail])
//
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//
// For more information, see http://www.boost.org 

// -----------------------------------------------------

#if !defined(BOOST_LAMBDA_EXCEPTIONS_HPP)
#define BOOST_LAMBDA_EXCEPTIONS_HPP

#include "boost/lambda/detail/control_constructs_common.hpp"

namespace boost { 
namespace lambda {

typedef lambda_functor<placeholder<EXCEPTION> > placeholderE_type;

namespace {
  boost::lambda::placeholderE_type freeE;
  boost::lambda::placeholderE_type& _e = freeE;        
}

// -- exception related actions -------------------

// catch actions.
template <class Catch1, class Catch2 = null_type, class Catch3 = null_type, 
          class Catch4 = null_type, class Catch5 = null_type, 
          class Catch6 = null_type, class Catch7 = null_type, 
          class Catch8 = null_type, class Catch9 = null_type, 
          class Catch10 = null_type>
struct catch_action {};

struct catch_all_action {};

template<class CatchActions>
struct return_try_catch_action {};

template<class CatchActions>
struct try_catch_action {};

// rethrow actions
struct throw_new_action {};
struct rethrow_action {};

template<class ThrowType> struct throw_action;

template<>
struct throw_action<rethrow_action> {
  template<class RET>
  static RET apply() {
    throw;
  }
};

template<> struct throw_action<throw_new_action> {
  template<class RET, class T>
  static RET apply(T& t) {
    throw t;
  }
};

// return types for throw_actions --------------------------------------------

template<class T, class Any>
struct 
return_type_N<throw_action<T>, Any> {
  typedef void type;
};


// return types deductions -------------------------------------------------

// the return type of try_catch is the return type of the try lambda_functor
// (the return types of try and catch parts must match unless try returns void
// or the catch part throws for sure)

// NOTE, the exception placeholder deduction rule is defined 
// in return_type_traits.hpp



// defined in control_constructs
class ifthenelse_action;

namespace detail {

// Templates for deducing, wether a lambda_functor throws inevitably of not -
// This mechanism is needed to make the compiler happy about
// return types of try and catch parts. 

// a lambda_functor throws for sure if:
//  - it is a throw expression
//  - it is a comma expression, and one of its arguments throws for sure
//  - it is an if_then_else expression and either the if statement or both 
//  the then and  else throw.
// (there are other cases as well, but we do not cover them)
// e.g. _1 + (rethrow(), 3) does throw for sure but this is not checked
// This implies, that in such a case, the return types of try and catch parts 
// must match if the try part returns other than void.
// (Such checks could be done though)

template <class Arg> 
struct throws_for_sure_phase2 {
  static const bool value = false;
};

template <int N, class ThrowType, class Args> 
struct throws_for_sure_phase2<
  lambda_functor< 
    lambda_functor_base<action<N, throw_action<ThrowType> >, Args> 
  > 
>
{
  static const bool value = true;
};

// Both then and else or the if throw of an if_then_else.
template <class Args> 
struct throws_for_sure_phase2<
  lambda_functor<
    lambda_functor_base<
      ifthenelse_action, Args
    > 
  > 
>
{
  static const bool value =
    throws_for_sure_phase2<
      typename boost::tuples::element<0, Args>::type>::value
    ||  
    (
       throws_for_sure_phase2<
         typename boost::tuples::element<1, Args>::type
       >::value
       && 
       throws_for_sure_phase2<
         typename boost::tuples::element<2, Args>::type
       >::value
    );
};

template <class Args> 
struct throws_for_sure_phase2<
  lambda_functor< 
    lambda_functor_base< other_action<comma_action>, Args> 
  > 
>
{
  static const bool value =
    throws_for_sure_phase2<
      typename boost::tuples::element<0, Args>::type
    >::value
    || 
    throws_for_sure_phase2<
      typename boost::tuples::element<1, Args>::type
    >::value;
};

  // get rid of any qualifiers and references
  // lambda_functors should be stored like that, so this is to be extra sure 
template <class Arg> 
struct throws_for_sure {
  static const bool value 
    = throws_for_sure_phase2<
        typename detail::remove_reference_and_cv<Arg>::type
      >::value;
};


// -- return_or_throw templates -----------------------------

// false case, catch and try return types are incompatible
// Now the catch part must throw for sure, otherwise a compile time error
// occurs.
template<bool is_conversion>
struct return_or_throw_phase2 {
  template<class RET, class Arg, CALL_TEMPLATE_ARGS>
  static RET call(Arg& arg, CALL_FORMAL_ARGS) {
    BOOST_STATIC_ASSERT(throws_for_sure<Arg>::value);
    detail::select(arg, CALL_ACTUAL_ARGS); // this line throws
    throw 1; // this line is never performed, hence 1 is just a dummy
             // The line is needed to make compiler happy and not require
             // a matching return type
  }
};

// the try and catch return types are compatible
template<>
struct return_or_throw_phase2<true> {
  template<class RET, class Arg, CALL_TEMPLATE_ARGS>
  static RET call(Arg& arg, CALL_FORMAL_ARGS) {
    return detail::select(arg, CALL_ACTUAL_ARGS);
  }
};


// the non-void case. Try part returns a value, so catch parts must 
// return a value of the same type or throw
template<class RET, class ARG>
struct return_or_throw {
  // Arg should be equal to ARG except that ARG may be a reference
  // to be sure, that there are no suprises for peculiarly defined return types
  // ARG is passed explicitely
  template<class Arg, CALL_TEMPLATE_ARGS>
  static RET call(Arg& arg, CALL_FORMAL_ARGS)
  {        
    //    typedef typename Arg::return_type<ARG, open_args<A&, B&, C&> >::type RT;        
    typedef typename as_lambda_functor<ARG>::type lf_type;
    typedef typename lf_type::inherited::template 
      sig<tuple<CALL_REFERENCE_TYPES> >::type RT;  

    return 
      return_or_throw_phase2<
        ::boost::is_convertible<RT, RET>::value
      >::template call<RET>(arg, CALL_ACTUAL_ARGS);
  }
};

// if try part returns void, we do not return the catch parts either
template<class ARG>
struct return_or_throw<void, ARG> {
  template<class Arg, CALL_TEMPLATE_ARGS>
  static void call(Arg& arg, CALL_FORMAL_ARGS) { detail::select(arg, CALL_ACTUAL_ARGS); }
};

} // end detail

// Throwing exceptions ---------------------------------------------

namespace detail {

template <class T> struct catch_block {}; 
struct catch_all_block {};

template <class T> struct exception_catch_tag {};

// normal catch block is represented as
// tagged_lambda_functor<exception_catch_tag<catch_type<T> > >, LambdaFunctor>
  
// the default catch all block as:
// tagged_lambda_functor<exception_catch_tag<catch_all_block> >, LambdaFunctor>


} // end detail

// the code is RETHROW, this ensures that a compile time error results, 
// if this lambda_functor is used outside a delayed catch_expression
inline const 
lambda_functor< 
  lambda_functor_base< 
    action<0, throw_action<rethrow_action> >, 
    null_type
  > 
>
rethrow() { 
  return 
      lambda_functor_base< 
        action<0, throw_action<rethrow_action> >,
        null_type
      > 
    ( null_type() );
}

template <class Arg1>
inline const 
lambda_functor<
  lambda_functor_base< 
    action<1, throw_action<throw_new_action> >, 
    tuple<typename const_copy_argument<const Arg1>::type>
  > 
>
throw_exception(const Arg1& a1) { 
  return 
      lambda_functor_base< 
        action<1, throw_action<throw_new_action> >, 
        tuple<typename const_copy_argument<const Arg1>::type>
      > 
    ( tuple<typename const_copy_argument<const Arg1>::type>(a1));
}

// create catch blocks
template <class CatchType, class Arg>
inline const 
tagged_lambda_functor<
  detail::exception_catch_tag<detail::catch_block<CatchType> >, 
  lambda_functor<Arg> 
> 
catch_exception(const lambda_functor<Arg>& a) { 
  // the third placeholder cannot be used in catch_exception
  //    BOOST_STATIC_ASSERT((!has_placeholder<Arg, THIRD>::value));
  return 
    tagged_lambda_functor<
      detail::exception_catch_tag<detail::catch_block<CatchType> >, 
      lambda_functor<Arg> 
    > (a);
}

// catch and do nothing case.
template <class CatchType>
inline const 
tagged_lambda_functor<
  detail::exception_catch_tag<detail::catch_block<CatchType> >, 
  lambda_functor<
    lambda_functor_base<
      do_nothing_action,
      null_type
    > 
  >
>
catch_exception() { 
  return 
    tagged_lambda_functor<
      detail::exception_catch_tag<detail::catch_block<CatchType> >, 
      lambda_functor<
        lambda_functor_base<
          do_nothing_action,
          null_type
        > 
      >
    > ();
}

// create catch(...) blocks
template <class Arg>
inline const 
tagged_lambda_functor<
  detail::exception_catch_tag<detail::catch_all_block>, 
  lambda_functor<Arg> 
> 
catch_all(const lambda_functor<Arg>& a) { 
  // the third placeholder cannot be used in catch_exception
  BOOST_STATIC_ASSERT((!has_placeholder<Arg, THIRD>::value));
  return 
    tagged_lambda_functor<
      detail::exception_catch_tag<detail::catch_all_block>, 
      lambda_functor<Arg> 
    > (a);
}

// catch(...) and do nothing case.
inline const 
tagged_lambda_functor<
  detail::exception_catch_tag<detail::catch_all_block>,