Fix for boost serialization

[efp]

When compiling with boost serialization versions 1.60.0 and up, one will
get an error that boost can't access the memblock destructor. This adds
the required friend statement for boost.

[slayoo]

Thank you! Let me keep it open for a few days and add a new Boost example to the continuous integration build beforehand so the fix would then also be exemplified.

[efp]

I tried this program

#define BZ_HAVE_BOOST_SERIALIZATION

#include <blitz/array.h>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>

#include <iostream>
#include <sstream>

int main()
{
    std::stringstream ss ;
    
    blitz::TinyVector<int, 3> dims{1,1,1} ;
    blitz::Array<float, 3> array(dims) ;
    array(0,1,0) = 3 ;
    
    boost::archive::text_oarchive oa(ss);
    oa << array ;
    
    std::cout << ss.str() << std::endl ;
    
    ss.seekg(0) ;
    blitz::Array<float, 3> array2(dims) ;    
    boost::archive::text_iarchive ia(ss);
    
    ia >> array2 ;
    
    std::cout << array2(0,1,0) << std::endl ;
}

On Ubuntu 18.04 gcc 7.3.0

g++ -o bstest -I. -lblitz bstest.cpp -lboost_serialization

Before fix:

/usr/local/include/boost/archive/detail/iserializer.hpp:246:17: error: ‘blitz::MemoryBlock<P_type>::~MemoryBlock() [with P_type = float]’ is protected within this context

After the fix, builds and runs with output:

22 serialization::archive 15 0 0 0 0 2 1 0
0 1 0.000000000e+00 0 0 0 3 1 1 1 0 0 0 0 0 3 1 1 1 3 2 1 0 3 0 0 0 0 0 3 1 1 1 0
0

Ok, that last number isn't right... I never tried it with a stringstream before.

Oddly, it fails to link with boost serialization unless I put the -lboost_serialization after the cpp file name.

Also note, the error only occurs when using the input archive; I tried it first with only the output archive and it compiled.

[slayoo]

thank you!

[citibeth]

@slayoo Can we merge this?

[slayoo]

As above, I vote for adding at least a minimalistic test case

[efp]

Since this fixes a compilation error, it doesn't seem amenable for addition to the test suite.

[slayoo]

Sorry, here's a PR that should hopefully fix the merge conflict: #165

[slayoo]

merged, thank you!