[Boost-users] Nested If in boost:mpl::if_

2 Dec 2010

      hi all

I am trying to use mpl to do some simple type computation that involves nest
if statements

The logic is somewhat like

if(T is Libor)
    return LiborType
if(
   or(
      or(T = Euribor,
         T = EURLibor),
      is_base_of(T, Libor)
    ),
    ConstrType2,
    if(
        or(is_base_of(T, Euribor),
           is_base_of(T, EURLibor)),
       ConstrType1,
       ConstrType
      )
   )

When I first coded it and instantiate T with some derived class of
Libor, the final type is always a generic type. Few more testing shows
that the inner if_ in the code below

   typedef typename
      boost::mpl::if_
      <
          boost::is_same<InType, QuantLib::Libor>,
          QuantLib::Libor,
          boost::mpl::if_
          <
                  boost::mpl::or_
                  <
                      boost::is_same<InType, QuantLib::Euribor>,
                      boost::is_same<InType, QuantLib::EURLibor>,
                      boost::is_base_of<QuantLib::Libor, InType>
                  >
              ConstrType2,
              boost::mpl::if_
              <
                  boost::mpl::or_
                  <
                      boost::is_base_of<QuantLib::Euribor, InType>,
                      boost::is_base_of<QuantLib::EURLibor, InType>
                  >,
                  ConstrType1,
                  ConstrType
              >
          >
      >::type Type;

does not reduce to ConstrType1/ConstrType2/ConstrType but the whole is
used as a type. So the final Type is just a type with 3 nested if_
class inside. I tried linearising the logic but this introduces other
problem. Is this a bug or a limitation of mpl::if_?

Thanks

[Boost-users] Nested If in boost:mpl::if_

Leon Sit