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

Subject: Re: [Boost-users] Nested If in boost:mpl::if_
From: Matt Calabrese (rivorus_at_[hidden])
Date: 2010-12-02 16:57:06

On Thu, Dec 2, 2010 at 3:09 PM, Leon Sit <wing1127aishi_at_[hidden]> wrote:

>
> 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_?
>
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It's not a limitation of mpl::if_, it's doing exactly what you are telling
it to do. What you actually want is to have your top-level mpl::if to
actually be mpl::eval_if, and you should be wrapping the second parameter,
"QuantLib::Libor" in mpl::identity. eval_if will automatically yield the
nested type of the result, which is necessary if you want the result of the
top-level condition to be the result of an inner conditions (otherwise, the
result of the top-level condition will be the inner condition itself, which
is what you see).

This has effectively the same result as not using eval_if, but still using
mpl::identity as I described only having "::type::type" as opposed to
"::type" at the end.

-- 
-Matt Calabrese