Dear all!
I have to do a lot of looping over TObjArray. I was thinking about using boost’s foreach macro:
boost.org/doc/libs/1_39_0/do … reach.html
Did anybody try to extend boost to allow looping over TObjArray or other root collections?
boost.org/doc/libs/1_39_0/do … ility.html
Thanks in advance,
Sebastian
Hi,
I do not know whether it has been done. However the member function Begin and End and the typedef TObjArray::Iterator_t are the ingredient you will need to implement it.
Cheers,
Philippe.
Hi Philippe!
Unfortunately I don’t find Begin and End member functions. Neither in TObjArray(Iter) nor TIterator (I checked the source). I’m also wondering if an operator++ is missing.
Thanks,
Sebastian
PS: I’m using v5-26-00b, but I also don’t see and Begin/End in root.cern.ch/svn/root/trunk
Hi,
Begin and End are defined in one the base class (TCollection) and the iterator for TObjArray (TObjArrayIter) does inherit from std::iterator should it should work properly (because the internal storage of TObjArray is similar to the storage for a vector<TObject*>)
Cheers,
Philippe.
Hi!
Thanks. TIter is a bit hidden. The implementation so far:
// foreach_TObjArray.cc
#include <iostream>
#include <boost/foreach.hpp>
#include "TObjArray.h"
#include "TVector3.h"
using namespace ROOT;
TIter range_begin( const TObjArray & x ) {
return TIter(&x).Begin();
}
TIter range_end( const TObjArray & x ) {
return TIter(&x).End();
}
bool operator==(const TIter& lhs, const TIter& rhs) {
return !(lhs != rhs);
}
namespace boost
{
// specialize range_mutable_iterator and range_const_iterator in namespace boost
template<>
struct range_mutable_iterator< TObjArray >
{
typedef TIterCategory<TObjArray> type;
};
}
int main() {
TObjArray objArray;
objArray.Add(new TVector3(1,2,3));
boost::BOOST_FOREACH(TObject* s, objArray) {
std::cout << s << '\n';
}
}I couldn’t find a const version of TIter, but I’m not sure if that’s a problem.
I compile it like this:
g++ `root-config --libs --cflags` -I/usr/include/boost foreach_TObjArray.cc -o foreach_TObjArrayBut I get the following error during compilation:
foreach_TObjArray.cc: In function ‘int main()’:
foreach_TObjArray.cc:43: error: expected unqualified-id before ‘if’
foreach_TObjArray.cc:43: error: expected ‘;’ before ‘if’
foreach_TObjArray.cc:43: error: ‘else’ without a previous ‘if’
foreach_TObjArray.cc:43: error: ‘_foreach_col43’ was not declared in this scope
foreach_TObjArray.cc:43: error: invalid conversion from ‘const TObject*’ to ‘TObject*’
In file included from foreach_TObjArray.cc:2:
/usr/local/include/boost/foreach.hpp: In function ‘typename boost::foreach_detail_::foreach_reference<T, C>::type boost::foreach_detail_::deref(const boost::foreach_detail_::auto_any_base&, boost::foreach_detail_::type2type<T, C>*) [with T = TObjArray, C = mpl_::bool_<false>]’:
foreach_TObjArray.cc:43: instantiated from here
/usr/local/include/boost/foreach.hpp:750: error: invalid initialization of non-const reference of type ‘const TObject*&’ from a temporary of type ‘TObject*’Any idea why
error: invalid initialization of non-const reference of type ‘const TObject*&’ from a temporary of type ‘TObject*’happens?
Thanks,
Sebastian
Hi,
I don’t know for sure but is likely linked to :[quote]foreach_TObjArray.cc:43: error: invalid conversion from ‘const TObject*’ to ‘TObject*’[/quote]. You would need to look carefully at the boost implementation to figure this out.
Cheers,
Philippe.
Hi!
Just for the record.
error: invalid conversion from ‘const TObject*’ to ‘TObject*’disappears changing
boost::BOOST_FOREACH(TObject* s, objArray)to
boost::BOOST_FOREACH(const TObject* s, objArray)but the other error stays.
Cheers,
Sebastian
First things first 
. Where does[quote]foreach_TObjArray.cc:43: error: expected unqualified-id before ‘if’[/quote] come from?
Philippe.
Hi!
You are right. The “boost::” in front of the macro is of course wrong. Here is the version which has only the last error.
#include <iostream>
#include <boost/foreach.hpp>
#include "TObjArray.h"
#include "TVector3.h"
//using namespace ROOT;
TIterCategory<TObjArray> range_begin( TObjArray & x ) {
return TIterCategory<TObjArray>(&x).Begin();
}
TIterCategory<TObjArray> range_end( TObjArray & x ) {
return TIterCategory<TObjArray>(&x).End();
}
/*
TIterCategory<TObjArray> range_begin( TObjArray const & x ) {
return TIterCategory<TObjArray>(&x).Begin();
}
TIterCategory<TObjArray> range_end( TObjArray const & x ) {
return TIterCategory<TObjArray>(&x).End();
}
*/
bool operator==(const TIterCategory<TObjArray>& lhs, const TIterCategory<TObjArray>& rhs) {
return !(lhs != rhs);
}
namespace boost
{
// specialize range_mutable_iterator and range_const_iterator in namespace boost
template<>
struct range_mutable_iterator<TObjArray >
{
typedef TIterCategory<TObjArray> type;
};
template<>
struct range_const_iterator<TObjArray >
{
typedef TIterCategory<TObjArray> type;
};
}
int main() {
TObjArray objArray;
objArray.Add(new TVector3(1,2,3));
BOOST_FOREACH(const TObject* s, objArray) {
std::cout << s << '\n';
}
}$ g++ -Wall `root-config --libs --cflags` -I/usr/include/boost foreach_TObjArray.cc -o foreach_TObjArray
In file included from foreach_TObjArray.cc:2:
/usr/local/include/boost/foreach.hpp: In function ‘typename boost::foreach_detail_::foreach_reference<T, C>::type boost::foreach_detail_::deref(const boost::foreach_detail_::auto_any_base&, boost::foreach_detail_::type2type<T, C>*) [with T = TObjArray, C = mpl_::bool_<false>]’:
foreach_TObjArray.cc:66: instantiated from here
/usr/local/include/boost/foreach.hpp:750: error: invalid initialization of non-const reference of type ‘const TObject*&’ from a temporary of type ‘TObject*’/usr/local/include/boost/foreach.hpp:750
template<typename T, typename C>
inline BOOST_DEDUCED_TYPENAME foreach_reference<T, C>::type
deref(auto_any_t cur, type2type<T, C> *)
{
typedef BOOST_DEDUCED_TYPENAME foreach_iterator<T, C>::type iter_t;
return *auto_any_cast<iter_t, boost::mpl::false_>(cur);
}(the return is line 750)
The preprocessor (g++ -E …) turns the macro into:
int main() {
TObjArray objArray;
objArray.Add(new TVector3(1,2,3));
if (boost::foreach_detail_::auto_any_t _foreach_col66 = boost::foreach_detail_::contain( (objArray) , (true ? 0 : boost::foreach_detail_::or_( boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost::foreach_detail_::is_array_(objArray)) , (true ? 0 : boost::foreach_detail_::is_rvalue_( (true ? boost::foreach_detail_::make_probe(objArray) : (objArray)), 0))) , boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost_foreach_is_noncopyable( boost::foreach_detail_::to_ptr(objArray) , boost_foreach_argument_dependent_lookup_hack_value)) , boost_foreach_is_lightweight_proxy( boost::foreach_detail_::to_ptr(objArray) , boost_foreach_argument_dependent_lookup_hack_value)))))) {} else if (boost::foreach_detail_::auto_any_t _foreach_cur66 = boost::foreach_detail_::begin( _foreach_col66 , (true ? 0 : boost::foreach_detail_::encode_type(objArray, boost::foreach_detail_::is_const_(objArray))) , (true ? 0 : boost::foreach_detail_::or_( boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost::foreach_detail_::is_array_(objArray)) , (true ? 0 : boost::foreach_detail_::is_rvalue_( (true ? boost::foreach_detail_::make_probe(objArray) : (objArray)), 0))) , boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost_foreach_is_noncopyable( boost::foreach_detail_::to_ptr(objArray) , boost_foreach_argument_dependent_lookup_hack_value)) , boost_foreach_is_lightweight_proxy( boost::foreach_detail_::to_ptr(objArray) , boost_foreach_argument_dependent_lookup_hack_value)))))) {} else if (boost::foreach_detail_::auto_any_t _foreach_end66 = boost::foreach_detail_::end( _foreach_col66 , (true ? 0 : boost::foreach_detail_::encode_type(objArray, boost::foreach_detail_::is_const_(objArray))) , (true ? 0 : boost::foreach_detail_::or_( boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost::foreach_detail_::is_array_(objArray)) , (true ? 0 : boost::foreach_detail_::is_rvalue_( (true ? boost::foreach_detail_::make_probe(objArray) : (objArray)), 0))) , boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost_foreach_is_noncopyable( boost::foreach_detail_::to_ptr(objArray) , boost_foreach_argument_dependent_lookup_hack_value)) , boost_foreach_is_lightweight_proxy( boost::foreach_detail_::to_ptr(objArray) , boost_foreach_argument_dependent_lookup_hack_value)))))) {} else for (bool _foreach_continue66 = true; _foreach_continue66 && !boost::foreach_detail_::done( _foreach_cur66 , _foreach_end66 , (true ? 0 : boost::foreach_detail_::encode_type(objArray, boost::foreach_detail_::is_const_(objArray)))); _foreach_continue66 ? boost::foreach_detail_::next( _foreach_cur66 , (true ? 0 : boost::foreach_detail_::encode_type(objArray, boost::foreach_detail_::is_const_(objArray)))) : (void)0) if (boost::foreach_detail_::set_false(_foreach_continue66)) {} else for (const TObject* s = boost::foreach_detail_::deref( _foreach_cur66 , (true ? 0 : boost::foreach_detail_::encode_type(objArray, boost::foreach_detail_::is_const_(objArray)))); !_foreach_continue66; _foreach_continue66 = true) {
std::cout << s << '\n';
}
}The error itself happens for code like this:
int* f() {
int a = 3;
return &a;
}
int main() {
const int*& rint = f();
}I know this turns into an academic exercise. But I would like to solve the puzzle.
Thanks in advance,
Sebastian
Hi,
Did you try when implemented the range_begin and range_end that takes non const parameter?
Philippe.
Hi!
The last version I’ve posted uses range_begin/end( TObjArray & x ) The const functions are commented.
The error stays the same if I have both, the const and non-const functions.
Could it be a problem that there is no const version of TIter(Category). The example:
boost.org/doc/libs/1_39_0/do … ility.html
has std::string::const_iterator
in
inline std::string::const_iterator range_begin( sub_string const & x )I’ve also tried “Making BOOST_FOREACH Work with Non-Copyable Sequence Types”. Error is the same. However a pointer to TObject is certainly copyable.
Thanks,
Sebastian
Hi,
[quote]Could it be a problem that there is no const version of TIter(Category). The example:
[/quote]It is plausible. Alternatively, it look like one need to find a way to make foreach_reference<T, C>::typebe “TObject*&” rather than a const.
Cheers,
Philippe.
Hi!
I ended up using the R__FOR_EACH macro defined in TCollection.h.
Cheers,
Sebastian
Perhaps you’re still interested in this, even though it’s been ten months since your post. I think the basic impediment to getting BOOST_FOREACH to work with a TObjArray is that dereferencing a TIterator returns a TObject * and not a TObject *&. The type detection machinery in BOOST_FOREACH works fine with standard-conforming iterators. I’m no C++ language lawyer, but TIterators don’t seem to be standard-conforming. The C++98 standard (24.1.3) says that the result of *a, where a is an iterator, should be T&.
It’s not an ideal solution, but you can get things to work by crafting a specialization of the “deref” function used by BOOST_FOREACH. You need to get it to do the impedance matching between what TIterator provides and what BOOST_FOREACH is expecting. If you add this to your example
namespace boost
{
namespace foreach_detail_
{
template<>
foreach_reference<TObjArray, mpl_::bool_<false> >::type
deref(auto_any_t cur, type2type<TObjArray, mpl_::bool_<false> >*)
{
TIterCategory<TObjArray> it = auto_any_cast<foreach_iterator<TObjArray,
mpl_::bool_<false> >::type, boost::mpl::false_>(cur);
const TObject* p = *it;
const TObject *&q = reinterpret_cast<const TObject *&>(p);
return q;
}
}
}which isn’t very pretty, I admit, then your code compiles and runs. For me. Today.
It would be cleaner and easier if dereferencing a TIterator just returned TObject *&.