filter_iterator and bind

Nico Galoppo

21 Feb 2006 21 Feb '06

1:42 p.m.

Hi, I'm having trouble getting make_filter_iterator and bind to work together nicely: ------------------------------------------------------------------------------- boost::function is_constraint; is_constraint = boost::bind(&node_type::IsConstraint, _1); boost::make_filter_iterator(is_constraint, ab.begin(), ab.end()); // ERROR: does not compile boost::make_filter_iterator(boost::bind(&node_type::IsConstraint, _1), ab.begin(), ab.end()); // compiles ------------------------------------------------------------------------------- Note that ab.begin()/ab.end() return iterators to containers of shared pointers. See below for compiler errors. What I would like to do, in the end, is something like this: ------------------------------------------------------------------------------- typedef boost::filter_iterator, articulated_model_type::node_df_traversal_iterator> joint_iterator; joint_iterator first = boost::make_filter_iterator(boost::bind(&node_type::IsConstraint, _1), ab.begin(), ab.end()); ------------------------------------------------------------------------------- Unfortunately, this doesn't compile either. I want an explicit handle to the interator (first), because I'd like to do a normal for loop like this: for(joint_iterator joint = first; joint != last; ++joint) { ... } Again, compile errors are below. Thanks for the help. --nico d:\dev\boost_1_33_1\boost\iterator\filter_iterator.hpp(100) : error C2664: 'boost::function1::result_type boost::function1::operator ()(T0) const' : cannot convert parameter 1 from 'Hybrid::Graph::const_node_ptr' to 'const Hybrid::Node ' with [ R=bool, T0=const Hybrid::Node::graph_type,ArticulatedModelNodeTraits<MyTypes>> , Allocator=std::allocator<void> ] and [ node_traits=ArticulatedModelNodeTraits<MyTypes> ] and [ graph_type_=Hybrid::Graph::graph_type, node_traits=ArticulatedModelNodeTraits<MyTypes> ] Reason: cannot convert from 'Hybrid::Graph::const_node_ptr' to 'const node_type' with [ node_traits=ArticulatedModelNodeTraits<MyTypes> ] No constructor could take the source type, or constructor overload resolution was ambiguous d:\dev\boost_1_33_1\boost\iterator\filter_iterator.hpp(99) : while compiling class-template member function 'void boost::filter_iterator::satisfy_predicate(void)' with [ Predicate=boost::function, Iterator=Hybrid::Graph::node_df_traversal_iterator ] d:\dev\Hybrid\Tests\Graph\main.cpp(645) : see reference to class template instantiation 'boost::filter_iterator' being compiled with [ Predicate=boost::function, Iterator=Hybrid::Graph::node_df_traversal_iterator ] ====================================================================================== :\dev\Hybrid\Tests\Graph\main.cpp(646) : error C2440: 'initializing' : cannot convert from 'boost::filter_iterator' to 'boost::filter_iterator' with [ Predicate=boost::_bi::bind_t,boost::_bi::list1>::B1>>, Iterator=Hybrid::Graph::node_df_traversal_iterator ] and [ Predicate=boost::function, Iterator=Hybrid::Graph::node_df_traversal_iterator ] No constructor could take the source type, or constructor overload resolution was ambiguous -- nico galoppo von borries @ address: 105 creel st., chapel hill comp. graphics phd. student @ north carolina, 27516 USA UNC, chapel hill @ phone: +1 (919) 962-1898 (office) @ +1 (919) 942-7609 (home) @ email: nico at cs dot unc dot edu @ homepage: http://www.cs.unc.edu/~nico --- debian linux :: vim powered

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David Abrahams

21 Feb 21 Feb

5:51 p.m.

Nico Galoppo writes:

...

I'm having trouble getting make_filter_iterator and bind to work together nicely:

------------------------------------------------------------------------------- boost::function is_constraint; is_constraint = boost::bind(&node_type::IsConstraint, _1);

boost::make_filter_iterator(is_constraint, ab.begin(), ab.end()); // ERROR: does not compile boost::make_filter_iterator(boost::bind(&node_type::IsConstraint, _1), ab.begin(), ab.end()); // compiles -------------------------------------------------------------------------------

Note that ab.begin()/ab.end() return iterators to containers of shared pointers. See below for compiler errors.

It's actually not bind, but function. Bind contains magic that treats shared_ptr<T> and T& the same way, but for function to take advantage of that magic, you need to make sure its argument type is shared_ptr<T>, not T&: boost::function)> is_constraint = boost::bind(&node_type::IsConstraint, _1); boost::make_filter_iterator(is_constraint, ab.begin(), ab.end()); The hint is right here:

...

Reason: cannot convert from 'Hybrid::Graph::const_node_ptr' to 'const node_type' with [ node_traits=ArticulatedModelNodeTraits<MyTypes> ]

HTH, -- Dave Abrahams Boost Consulting www.boost-consulting.com

Nico Galoppo

22 Feb 22 Feb

1:42 a.m.

David Abrahams wrote:

...

...
I'm having trouble getting make_filter_iterator and bind to work together nicely:

------------------------------------------------------------------------------- boost::function is_constraint; is_constraint = boost::bind(&node_type::IsConstraint, _1);

boost::make_filter_iterator(is_constraint, ab.begin(), ab.end()); // ERROR: does not compile boost::make_filter_iterator(boost::bind(&node_type::IsConstraint, _1), ab.begin(), ab.end()); // compiles -------------------------------------------------------------------------------

Note that ab.begin()/ab.end() return iterators to containers of shared pointers. See below for compiler errors.

It's actually not bind, but function. Bind contains magic that treats shared_ptr<T> and T& the same way, but for function to take advantage of that magic, you need to make sure its argument type is shared_ptr<T>, not T&:

boost::function)> is_constraint = boost::bind(&node_type::IsConstraint, _1);

boost::make_filter_iterator(is_constraint, ab.begin(), ab.end());

Thanks, that works like a charm. Unfortunately, dereferencing the created iterator gives more trouble: boost::function)> is_constraint = boost::bind(&node_type::IsConstraint, _1); typedef boost::filter_iterator)>, articulated_model_type::node_df_traversal_iterator> joint_node_iterator; joint_node_iterator jointnode = boost::make_filter_iterator(is_constraint, ab.begin(), ab.end()); std::cout << jointnode->Model(); ///< this line fails to compile There seems to be a problem with const-ness (see below). Thanks again. --nico ------------------------------------------------------------------------------ d:\dev\boost_1_33_1\boost\iterator\iterator_adaptor.hpp(307) : error C2440: 'return' : cannot convert from 'Hybrid::Graph::const_node_ptr' to 'boost::iterator_facade::reference' with [ node_traits=Hybrid::ArticulatedModelNodeTraits<MyTypes> ] and [ Derived=boost::filter_iterator::node_type>)>,Hybrid::Graph::node_df_traversal_iterator>, Value=boost::iterator_value::node_df_traversal_iterator>::type, CategoryOrTraversal=boost::mpl::identityboost::forward_traversal_tag::type, Reference=boost::iterator_reference::node_df_traversal_iterator>::type, Difference=boost::iterator_difference::node_df_traversal_iterator>::type ] A reference that is not to 'const' cannot be bound to a non-lvalue d:\dev\boost_1_33_1\boost\iterator\iterator_adaptor.hpp(307) : while compiling class-template member function 'boost::iterator_facade::reference boost::iterator_adaptor::dereference(void) const' with [ Derived=boost::filter_iterator::node_type>)>,Hybrid::Graph::node_df_traversal_iterator>, Value=boost::iterator_value::node_df_traversal_iterator>::type, CategoryOrTraversal=boost::mpl::identityboost::forward_traversal_tag::type, Reference=boost::iterator_reference::node_df_traversal_iterator>::type, Difference=boost::iterator_difference::node_df_traversal_iterator>::type, Base=Hybrid::Graph::node_df_traversal_iterator, Traversal=boost::mpl::if_boost::forward_traversal_tag::type,boost::random_access_traversal_tag>,boost::bidirectional_traversal_tag,boost::use_default>::type ] d:\dev\boost_1_33_1\boost\iterator\filter_iterator.hpp(46) : see reference to class template instantiation 'boost::iterator_adaptor' being compiled with [ Derived=boost::filter_iterator::node_type>)>,Hybrid::Graph::node_df_traversal_iterator>, Base=Hybrid::Graph::node_df_traversal_ iterator, Value=boost::use_default, Traversal=boost::mpl::if_boost::forward_traversal_tag::type,boost::random_access_traversal_tag>,boost::bidirectional_traversal_tag,boost::use_default>::type ] d:\dev\Hybrid\Tests\Graph\main.cpp(398) : see reference to class template instantiation 'boost::filter_iterator' being compiled with [ Predicate=boost::function::node_type>)>, Iterator=Hybrid::Graph::node_df_traversal_iterator ] -- nico galoppo von borries @ address: 105 creel st., chapel hill comp. graphics phd. student @ north carolina, 27516 USA UNC, chapel hill @ phone: +1 (919) 962-1898 (office) @ +1 (919) 942-7609 (home) @ email: nico at cs dot unc dot edu @ homepage: http://www.cs.unc.edu/~nico --- debian linux :: vim powered

David Abrahams

3:35 p.m.

Nico Galoppo writes:

...

Thanks, that works like a charm. Unfortunately, dereferencing the created iterator gives more trouble:

boost::function)> is_constraint = boost::bind(&node_type::IsConstraint, _1); typedef boost::filter_iterator)>, articulated_model_type::node_df_traversal_iterator> joint_node_iterator;

joint_node_iterator jointnode = boost::make_filter_iterator(is_constraint, ab.begin(), ab.end());

std::cout << jointnode->Model(); ///< this line fails to compile

There seems to be a problem with const-ness (see below).

It's not a constness problem, exactly. The problem is that the result of *ab.begin() is an rvalue (i.e. returned by value, not by reference). Yet the filter_iterator thinks it is iterating over lvalues: its reference type is Hybrid::Graph::const_node_ptr&, and the compiler is complaining that you can't initialize such a reference with a non-lvalue. It's hard to come up with a complete analysis with the little information I have here, but I believe Hybrid::Graph::node_df_traversal_iterator is misreporting its reference type or its category. An iterator whose operator* returns by value cannot be a forward iterator; it can only be an input iterator. -- Dave Abrahams Boost Consulting www.boost-consulting.com

Nico Galoppo

4:38 p.m.

David Abrahams wrote:

...

It's not a constness problem, exactly. The problem is that the result of

*ab.begin()

is an rvalue (i.e. returned by value, not by reference). Yet the filter_iterator thinks it is iterating over lvalues: its reference type is Hybrid::Graph::const_node_ptr&, and the compiler is complaining that you can't initialize such a reference with a non-lvalue. It's hard to come up with a complete analysis with the little information I have here, but I believe

Hybrid::Graph
is misreporting its reference type or its category. An iterator whose operator* returns by value cannot be a forward iterator; it can only be an input iterator.

I must admit, I'm only a novice at writing my own iterators. I've given it a try (see below), but something must be doing something wrong as you said. I think operator*() returns a reference now, but I could be wrong. ------------------------------------------------------------------------------- class node_df_traversal_iterator : public std::iteratorstd::forward_iterator_tag,node_type { protected: node_ptr m_node; ///< Current node being visited in traversal. node_ptr_container m_queue; ///< Remaining unvisited nodes in traversal. public: node_df_traversal_iterator(node_ptr node) : m_node(node) { if(node) m_queue.push_back(node); } bool operator== ( node_df_traversal_iterator const & other ) const{ return (other.m_node==m_node); } bool operator!= ( node_df_traversal_iterator const & other ) const{ return !((*this)==other); } node_type & operator*() {return (*m_node);} node_ptr operator->() {return m_node;} node_type const & operator*() const {return (*m_node);} const_node_ptr operator->()const {return const_node_ptr(m_node);} node_df_traversal_iterator & operator++() { if(m_queue.empty()) { m_node.reset(); return (*this); } m_queue.pop_front(); node_ptr_iterator begin = m_node->child_ptr_begin(); node_ptr_iterator end = m_node->child_ptr_end(); for(node_ptr_iterator child = begin; child != end; ++child ) m_queue.push_front( *child ); // depth first if(m_queue.empty()) { m_node.reset(); } else m_node = m_queue.front(); return (*this); } }; node_df_traversal_iterator begin() { return node_df_traversal_iterator(m_root); } node_df_traversal_iterator end() { return node_df_traversal_iterator( node_ptr() ); } const node_df_traversal_iterator begin() const { node_ptr root = boost::const_pointer_cast(m_root); return node_df_traversal_iterator(root); } const node_df_traversal_iterator end() const { return node_df_traversal_iterator( node_ptr() ); } -- nico galoppo von borries @ address: 105 creel st., chapel hill comp. graphics phd. student @ north carolina, 27516 USA UNC, chapel hill @ phone: +1 (919) 962-1898 (office) @ +1 (919) 942-7609 (home) @ email: nico at cs dot unc dot edu @ homepage: http://www.cs.unc.edu/~nico --- debian linux :: vim powered

David Abrahams

5:36 p.m.

Nico Galoppo writes:

...

David Abrahams wrote:

...
It's not a constness problem, exactly. The problem is that the result of

*ab.begin()

is an rvalue (i.e. returned by value, not by reference). Yet the filter_iterator thinks it is iterating over lvalues: its reference type is Hybrid::Graph::const_node_ptr&, and the compiler is complaining that you can't initialize such a reference with a non-lvalue. It's hard to come up with a complete analysis with the little information I have here, but I believe

Hybrid::Graph
is misreporting its reference type or its category. An iterator whose operator* returns by value cannot be a forward iterator; it can only be an input iterator.

I must admit, I'm only a novice at writing my own iterators. I've given it a try (see below), but something must be doing something wrong as you said.

Novices should not write their own iterators without the help of boost::iterator_facade or iterator_adaptor. There are too many ways to get it wrong.

...

I think operator*() returns a reference now, but I could be wrong.

"Now" meaning you juste fixed it, or has it always been returning a reference? BTW, I also wonder if building your own graph classes is the best course of action when Boost provides a Graph library.

...

-------------------------------------------------------------------------------

class node_df_traversal_iterator : public std::iteratorstd::forward_iterator_tag,node_type { protected:

node_ptr m_node; ///< Current node being visited in traversal. node_ptr_container m_queue; ///< Remaining unvisited nodes in traversal.

public:

node_df_traversal_iterator(node_ptr node) : m_node(node) { if(node) m_queue.push_back(node); }

bool operator== ( node_df_traversal_iterator const & other ) const{ return (other.m_node==m_node); } bool operator!= ( node_df_traversal_iterator const & other ) const{ return !((*this)==other); } node_type & operator*() {return (*m_node);}

Yep, looks like a reference.

...

node_ptr operator->() {return m_node;} node_type const & operator*() const {return (*m_node);}

This is where your problem is. The const-ness of an iterator should never affect the constness of the elements it traverses. I suggest, strongly, that you go through the tutorial at http://www.boost.org/libs/iterator/doc/iterator_facade.html#tutorial-example and build your iterators around that. HTH, -- Dave Abrahams Boost Consulting www.boost-consulting.com

Nico Galoppo

23 Feb 23 Feb

4:49 a.m.

David Abrahams wrote:

...

I suggest, strongly, that you go through the tutorial at

http://www.boost.org/libs/iterator/doc/iterator_facade.html#tutorial-example

and build your iterators around that.

Wow, that tutorial was really helpful. I rewrote my iterators using iterator_facade<>, it was a breeze. Thanks! --nico -- nico galoppo von borries @ address: 105 creel st., chapel hill comp. graphics phd. student @ north carolina, 27516 USA UNC, chapel hill @ phone: +1 (919) 962-1898 (office) @ +1 (919) 942-7609 (home) @ email: nico at cs dot unc dot edu @ homepage: http://www.cs.unc.edu/~nico --- debian linux :: vim powered

yinglcs2＠yahoo.com

21 Feb 21 Feb

9:31 p.m.

New subject: How to reverse the logic of a Predicate in boost?

I have the following code which copy items if certain condition is met: copy_if(a.begin(), a.end(), back_inserter(b), bind( &::feq<float>, _1, max)) ); How can I reverse the logic of that? how can I call std::not1() in the boost lambda bind library? __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

Jeff Flinn

9:38 p.m.

New subject: How to reverse the logic of a Predicate in boost?

yinglcs2@yahoo.com wrote:

...

I have the following code which copy items if certain condition is met:

copy_if(a.begin(), a.end(), back_inserter(b), bind( &::feq<float>, _1, max)) );

How can I reverse the logic of that? how can I call std::not1() in the boost lambda bind library?

copy_if( a.begin() , a.end() , back_inserter(b) , !bind( &::feq<float>, _1, max ) ); Should do it, at least with 1.33.1, if that's what you mean by 'reverse the logic'. Jeff Flinn

Peter Dimov

10:04 p.m.

New subject: How to reverse the logic of a Predicate in boost?

yinglcs2@yahoo.com wrote:

...

I have the following code which copy items if certain condition is met:

copy_if(a.begin(), a.end(), back_inserter(b), bind( &::feq<float>, _1, max)) );

How can I reverse the logic of that?

Use !bind( &::feq<float>, _1, max )

yinglcs2＠yahoo.com

22 Feb 22 Feb

4:58 p.m.

New subject: How to call STL map.second in boost lambda?

I have a for loop which pass the map.second to a function, like this: class A; typedef map MyMap; sortY(A& a); for (MyMap::iterator iter = map.begin(); iter != map.end(); ++iter) { A *a = (*iter).second; sortY(*a); } how can I translate the above for() loop into for_each and use boost lambda? __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

Kevin Heifner

5:51 p.m.

New subject: How to call STL map.second in boost lambda?

yinglcs2@yahoo.com wrote:

...

I have a for loop which pass the map.second to a function, like this: class A; typedef map MyMap;

sortY(A& a);

for (MyMap::iterator iter = map.begin(); iter != map.end(); ++iter) { A *a = (*iter).second;

sortY(*a); }

how can I translate the above for() loop into for_each and use boost lambda?

I didn't test the following, but it should work :) #include #include using boost::lambda::_1; using boost::lambda::bind; std::for_each(map.begin(), map.end(), bind(&sortY, *bind(&MyMap::value_type::second, _1))); KevinH -- Kevin Heifner heifner @ ociweb.com http://heifner.blogspot.com Object Computing, Inc. (OCI) www.ociweb.com

yinglcs2＠yahoo.com

7:48 p.m.

New subject: How to call STL map.second in boost lambda?

I have this compile error: I did this: std::for_each(map.begin(), map.end(), bind( &BlockList::sortY, this, *bind(&MyMap::value_type::second, _1))); ../BlockList.cpp:769: error: no matching function for call to âbind(<unknown type>, const BlockList* const, const boost::lambda::lambda_functorboost::lambda::contentsof_action, boost::tuples::tuple >, boost::tuples::tuple, BlockDataList*>::* const, const boost::lambda::lambda_functor

...

, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > , boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >)â make: *** [BlockList.o] Error 1

--- Kevin Heifner wrote:

...

yinglcs2@yahoo.com wrote:

...
I have a for loop which pass the map.second to a function, like this: class A; typedef map MyMap;

sortY(A& a);

for (MyMap::iterator iter = map.begin(); iter != map.end(); ++iter) { A *a = (*iter).second;

sortY(*a); }

how can I translate the above for() loop into for_each and use boost lambda?

I didn't test the following, but it should work :)

#include #include

using boost::lambda::_1; using boost::lambda::bind;

std::for_each(map.begin(), map.end(), bind(&sortY, *bind(&MyMap::value_type::second, _1)));

KevinH -- Kevin Heifner heifner @ ociweb.com http://heifner.blogspot.com Object Computing, Inc. (OCI) www.ociweb.com _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org

http://lists.boost.org/mailman/listinfo.cgi/boost-users

...

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Kevin Heifner

8:13 p.m.

New subject: How to call STL map.second in boost lambda?

yinglcs2@yahoo.com wrote:

...

I have this compile error: I did this:

std::for_each(map.begin(), map.end(), bind( &BlockList::sortY, this, *bind(&MyMap::value_type::second, _1)));

Works for me, boost 1.33 VC7.1: class A{}; typedef std::map MyMap; class BlockList { public: void sortY(A& a) {} void doIt() { using boost::lambda::_1; using boost::lambda::bind; MyMap map; std::for_each(map.begin(), map.end(), bind( &BlockList::sortY, this, *bind(&MyMap::value_type::second, _1))); } }; KevinH -- Kevin Heifner heifner @ ociweb.com http://heifner.blogspot.com Object Computing, Inc. (OCI) www.ociweb.com

yinglcs2＠yahoo.com

7:57 p.m.

New subject: How to call STL map.second in boost lambda?

Sorry. That works. I made a mistake myself. --- Kevin Heifner wrote:

...

yinglcs2@yahoo.com wrote:

...
I have a for loop which pass the map.second to a function, like this: class A; typedef map MyMap;

sortY(A& a);

for (MyMap::iterator iter = map.begin(); iter != map.end(); ++iter) { A *a = (*iter).second;

sortY(*a); }

how can I translate the above for() loop into for_each and use boost lambda?

I didn't test the following, but it should work :)

#include #include

using boost::lambda::_1; using boost::lambda::bind;

std::for_each(map.begin(), map.end(), bind(&sortY, *bind(&MyMap::value_type::second, _1)));

KevinH -- Kevin Heifner heifner @ ociweb.com http://heifner.blogspot.com Object Computing, Inc. (OCI) www.ociweb.com _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org

http://lists.boost.org/mailman/listinfo.cgi/boost-users

...

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Daniel Mitchell

21 Feb 21 Feb

10:33 p.m.

New subject: How to reverse the logic of a Predicate in boost?

On Tuesday 21 February 2006 15:31, yinglcs2@yahoo.com wrote:

...

I have the following code which copy items if certain condition is met:

copy_if(a.begin(), a.end(), back_inserter(b), bind( &::feq<float>, _1, max)) );

How can I reverse the logic of that?

Consider using remove_copy_if instead of copy_if. Daniel

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Daniel Mitchell
David Abrahams
Jeff Flinn
Kevin Heifner
Nico Galoppo
Peter Dimov
yinglcs2＠yahoo.com