[Boost-users] [mpl] cross product of 2 sequences

From: Roman Perepelitsa (roman.perepelitsa_at_[hidden])
Date: 2007-11-21 03:20:55

Hello,

I need metafunction cross_product, which should
transform 2 sequences to a sequence of pairs.

Example:

typedef list<int, char> l1;
typedef list<int *, char *> l2;
typedef cross_product<l1, l2>::type c;
typedef list<
    pair<int, int *>,
    pair<int, char *>,
    pair<char, int *>,
    pair<char, char *>
> e;
BOOST_MPL_ASSERT((equal<c, e>));

The best definition I came up with is the
following:

template <class T, class R>
struct product : transform<R, pair<T, _1> >
{
};

template <class R1, class R2>
struct cross_product :
    fold<
        typename transform<R1, product<_1, R2> >::type,
        list<>,
        joint_view<_1, _2>
    >
{
};

Is there a better way to do it? How can I get rid of
'struct product' and implement it as one metafunction?

Regards,
Roman Perepelitsa

Deutsche Bank Moscow
[phone]

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