From: pongba (pongba_at_[hidden])
Date: 2006-03-14 00:25:14
Okay, just image some sort of code like this:
typedef mpl::vector_c<int,1,2,3> v;
result_value; // =123
Imaginably, the implementation of MPL_METAFUNC would involve BOOST_TYPEOF to
deduce the type of "_1*CONS(10)+_2" so as to construct a corresponding
metafunction, that is, "mpl::plus<_2,mpl::times<_1,int_<10> > >"
(CONS here is used to work around the embarrassment that 10 becomes sort of
variable when passed directly to operator*, so we use CONS(10) which expands
into something like "int_<10>()" which entirely preserve "10" at compile-time).
Arguably this is feasible, but I lack the time to implement it fully.
(although it would be pretty simple, e.g.
#define DEFINE_BINARY_OP(op,mpl_binray_op) \
template <typename T, typename U> \
mpl_binary_op<T,U> operator op (T t, U u) \
return mpl_binary_op<T,U>(); \
Admittedly, there exists a name confliction between mpl::_1 and lambda::_1
due to the inherent difference between type and variable in the language,
so we couldn't use the same _1 and _2 in both "plus<_1,_2>" and "_1+_2".
Any good remedies for that?(of course we could always turn to "_1()+_2()"
in which _1/2 means mpl::_1/2)
My question is:
Is this valuable?(IMO,it'll make arithmetic operation in metaprogramming much
easier and clearer, just watch "_1*10+_2" v.s.
"mpl::plus<_2,mpl::times<_1,int_<10> > >" you'll see that).
And if it is, would Dave consider adding it to MPL?
Thanks in advance!
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk