CODEWITHSUNDEEP
c++boostboost-mplboost-preprocessor
David
David

Reputation: 28178

Compile time initialization of array using boost pp & mpl

Given:

typedef boost::mpl::vector<Type1, Type2, Type3> types;
const size_t numTypes = boost::mpl::size<types>::value;
std::array<std::function<bool(const obj&, const obj&)>, numTypes*numTypes> arr;

I'm trying to get this sort of functionality in compile time:

for( size_t i = 0; i < numTypes; ++i )
{
    for( size_t j = 0; j < numTypes; ++j )
    {
        arr[i*numTypes+j] = ObjPair<boost::mpl::at_c<vecType, i>::type, boost::mpl::at_c<vecType, j>::type>::Foo;
    }
}

I think it would look something like:

std::array<std::function<bool(const obj&, const obj&)>, numTypes*numTypes> arr = { BOOST_PP_FOR((0, numTypes), PRED, OP, MACRO) };

But I can't get it working (I didn't post my full failed attempt at using BOOST_PP_FOR).

ObjPair<T1, T2>::Foo is a static method of signiture bool(const obj&, const obj&). It's specialized for different obj types.

I would be using this array to find a particular function given pairs of objects. The objects are held as their base classes, and I can index the array with some math to determine the index based on IDs available in the base class.

Upvotes: 2

Views: 967

Answers (1)

Arpegius
Arpegius

Reputation: 5887

It is not possible for PP to iterate over boost::mpl::vector size. Hovewer you can try define it.

typedef boost::mpl::vector<bool, short, long> vecType;
#define numTypes 3

I have no TR1 so I try with boost array:

typedef  boost::function<bool(const obj&, const obj&)> Function;
typedef boost::array<Function, numTypes*numTypes> FooArray;

#define OBJPAIR_FOO_ARRAY(z, n, text)  BOOST_PP_COMMA_IF(n) &ObjPair<      \
boost::mpl::at_c<vecType, n/numTypes>::type,  \
boost::mpl::at_c<vecType, n%numTypes>::type   \
    >::Foo

FooArray fooArray= {
    BOOST_PP_REPEAT( BOOST_PP_MUL(numTypes, numTypes) , OBJPAIR_FOO_ARRAY, )
};

Upvotes: 2

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