compiler error with DBSCAN code when using GCC 4

[twongjirad]

found by @drinkingkazu

initially show in Issue #82

But I do get a compiler error that looks like a compiler version issue while building DBSCANN algorithm:

In file included from DBSCANAlgo.cxx:3:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/algorithm:62:
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/stl_algo.h:2263:11: error: no matching function for call to object of type 'mycompare_t'
while (__comp(*__first, __pivot))
^~
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/stl_algo.h:2296:19: note: in instantiation of function template specialization
'std::__unguarded_partition<__gnu_cxx::__normal_iterator<std::pair<int, double> *, std::vector<std::pair<int, double>, std::allocator<std::pair<int, double> > > >,
std::pair<int, double>, mycompare_t>' requested here
return std::__unguarded_partition(__first + 1, __last, *__first, __comp);
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/stl_algo.h:2337:11: note: in instantiation of function template specialization
'std::__unguarded_partition_pivot<__gnu_cxx::__normal_iterator<std::pair<int, double> *, std::vector<std::pair<int, double>, std::allocator<std::pair<int, double> > > >,
mycompare_t>' requested here
std::__unguarded_partition_pivot(__first, __last, __comp);
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/stl_algo.h:5498:9: note: in instantiation of function template specialization
'std::__introsort_loop<__gnu_cxx::__normal_iterator<std::pair<int, double> *, std::vector<std::pair<int, double>, std::allocator<std::pair<int, double> > > >, long,
mycompare_t>' requested here
std::__introsort_loop(__first, __last,
^
DBSCANAlgo.cxx:264:12: note: in instantiation of function template specialization 'std::sort<__gnu_cxx::__normal_iterator<std::pair<int, double> *, std::vector<std::pair<int,
double>, std::allocator<std::pair<int, double> > > >, mycompare_t>' requested here
std::sort( hitlist.begin(), hitlist.end(), mycompare );
^
DBSCANAlgo.cxx:221:12: note: candidate function not viable: 2nd argument ('const std::pair<int, double>') would lose const qualifier
bool operator() ( std::pair<int,double>& lhs, std::pair<int,double>& rhs ) {
^
In file included from DBSCANAlgo.cxx:3:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/algorithm:62:

[twongjirad]

found by @vgenty

Same result as above on develop with GCC 4.8.4 on ubuntu 14.04.5

https://goo.gl/Uj8ZCE

[twongjirad]

moved struct outside of the function. @vgenty, @drinkingkazu does this help?

[vgenty]

Similar result...
https://goo.gl/AztwSK

[twongjirad]

How about now? The comparison operator is pass by copy now.

[vgenty]

Yes, build is fine now

[twongjirad]

Thanks!