Apply the same function to each data member - Transform on heterogeneous types sort of thing

Question

Consider the following struct:

struct Test {
   char a;
   short b;
   int c;
   long long d;
   void transformTest() {
      // Pseudo
      foreach datamember (regardless of type) of Test
          call someTransform(datamember)
   }
};

We could also pass a lambda, function pointer, functor, whatever into the transformTest(), that's not my concern as of right now.

What's the best way to do this?

Answer 1

The best way is to do it explicitly:

someTransform(a);
someTransform(b);
someTransform(c);
someTransform(d);

Of course, you'll need an appropriate number of overloads of someTransform().

If you really, really don't like that, there's always Boost Fusion. With that you can put your values together in a structure which the library understands and then can iterate over. This won't be worth doing for simple use cases.

Answer 2

Sounds like a case for Boost Fusion and its for_each() function combined with BOOST_FUSION_ADAPT_STRUCT. This stuff can work some miracles! Here's an example on how you can do it:

#include <boost/fusion/include/algorithm.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <iostream>

using namespace boost::fusion;

struct Print
{
    template <typename T>
    void operator()( T && t ) const
    {

        std::cout << t << ' ';
    }
};

struct Test {
    char a;
    short b;
    int c;
    long long d;

    void printTest() const;
};

BOOST_FUSION_ADAPT_STRUCT(
    Test,
    (char, a)
    (short, b)
    (int, c)
    (long long, d)
    )

void Test::printTest() const
{
    for_each ( *this, Print() );
}

int main()
{
    const auto t = Test();
    t.printTest();
}