On 19/05/07, Stephen Torri <storri@torri.org> wrote:

On Sat, 2007-05-19 at 09:34 -0400, Nat Goodspeed wrote:

...

...

-----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users- bounces@lists.boost.org] On Behalf Of Stephen Torri Sent: Friday, May 18, 2007 9:01 PM To: boost-users Subject: [Boost-users] Converting loop to using boost::lambda where containers has boost::shared_ptrs

My idea was to do:

std::for_each ( m_data.begin(), m_data.end(), output << (_1 ->* &Verification_Type_Info::to_String) ( new_indent_limit ) );

[Nat] I think the construct you want will look more like (untested):

std::for_each(m_data.begin(), m_data.end(), output << boost::bind(&Verification_Type_Info::to_String, _1, new_indent_limit));

Its close but not quite. I get an error message that _1 is ambiguous

Append_Frame.cpp:48: error: reference to '_1' is ambiguous /usr/include/boost/lambda/core.hpp:69: error: candidates are: const boost::lambda::placeholder1_type& boost::lambda::<unnamed>::_1 /usr/include/boost/bind/placeholders.hpp:54: error: boost::arg<1> <unnamed>::_1

Stephen

Nat's using Boost.Bind, not the bind in Boost.Lambda - they both define _1 as a placeholder, so they clash... Using bind from Boost.Lambda, you'll need nested binds to cope with shared_ptr: using namespace boost::lambda; std::for_each(m_data.begin(), m_data.end(), output << bind(&Verification_Type_Info::to_String, bind(boost::shared_ptr<Verification_Type_Info>::get, _1), new_indent_limit)); Totally untested.... HTH Stuart Dootson

On Sat, 2007-05-19 at 11:56 -0400, Nat Goodspeed wrote:

[Nat] Or you could explicitly qualify _1 in my version:

...boost::bind(&Verification_Type_Info::to_String, boost::bind::_1, new_indent_limit)...

I like that boost::bind() knows about shared_ptrs.

I did the following: std::for_each ( m_data.begin(), m_data.end(), output << boost::bind ( &Verification_Type_Info::to_String, boost::bind::_1, new_indent_limit ) ); I get an error that Append_Frame.cpp: In member function 'virtual std::string libreverse::java_module::Append_Frame::to_String(uint32_t) const': Append_Frame.cpp:50: error: 'boost::bind' is not a class or namespace Are you sure that the second argument is boost::bind::_1? I found that _1 is declared in boost/bind/placeholders.hpp as: boost::arg<1> _1; Stephen

-----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users- bounces@lists.boost.org] On Behalf Of Stephen Torri Sent: Saturday, May 19, 2007 12:58 PM To: boost-users@lists.boost.org Subject: Re: [Boost-users] Converting loop to usingboost::lambda where containers has boost::shared_ptrs

Here is a test program that represents the problem we are trying to solve.

std::for_each ( m_data.begin(), m_data.end(), std::cout << boost::bind ( &Base::to_String, boost::bind::_1, indent_value ) );

[Nat] Heh. With my VC 7.1 compiler (Version 13.10.3077 according to cl /help), the program you sent produces an ICE. But then I'm still on Boost 1.31.1. On the other hand, since the program you sent makes no mention whatsoever of boost::lambda, you can remove the boost::bind qualification from _1 because there's no ambiguity. I did that, and got an error about trying to insert a boost::bind() expression to std::cout. Which would sort of toss us back towards boost::lambda. I thought I'd try using boost::bind on the insertion operator anyway: std::for_each ( m_data.begin(), m_data.end(), boost::bind(operator<<, boost::ref(std::cout), boost::bind ( &Base::to_String, _1, indent_value ) )); but the compiler wasn't buying it. So... maybe there's a way to express what I was trying to write above, or maybe there's a way to express Stuart's boost::lambda::bind construct. But for myself, in this situation I'd consider an explicit 'for' loop the clearest expression of intent. C++ is a truly amazing language that, in many cases, *almost* gets you where you want to go. :-)

I am glad to know I still the have skill of breaking compilers. :)

Well, I seem to have similar skills. The code below crashes my compiler ( VC7.1 SP 1), as well. void print( const std::string& s ) { std::cout << s; } int main ( int, char** ) { typedef boost::shared_ptr<A> A_ptr_t; typedef boost::shared_ptr<D> D_ptr_t; typedef std::vector < boost::shared_ptr<Base> > Data_t; Data_t m_data; A_ptr_t a ( new A ( 50 ) ); D_ptr_t d ( new D ( 30 ) ); m_data.push_back ( a ); m_data.push_back ( d ); boost::uint32_t indent_value = 4; // this works boost::bind( &print , boost::bind( &Base::to_String , A_ptr_t( new A( 5 ) ) , indent_value ))(); // this doesn't work - ICE std::for_each ( m_data.begin(), m_data.end(), boost::bind( &print , boost::bind( &Base::to_String , boost::bind::_1 , indent_value ))); return 0; } I know this is not the solution. I'm still using a seperate function print() for outputting. I will keep trying to solve that one. On the other hand it would be nice if boost::bind comes some handy function like the print(). Just a thought. Christian

Ovanes, I know about the /ZmXXX compiler option. Usually the compiler will report when it's running out of heap space. But in this case the compiler just crashes. This is very simple example that crashes the compiler. #include <iostream> #include <string> #include <vector> #include <boost/shared_ptr.hpp> #include <boost/bind.hpp> void print( const std::string* s ) { std::cout << s; } int main ( int, char** ) { typedef boost::shared_ptr<std::string> string_ptr_t; typedef std::vector < string_ptr_t > vec_t; vec_t data; // this works boost::bind( &print , boost::bind( &string_ptr_t::get , string_ptr_t( new std::string( "Hello" ))))(); // this doesn't work - ICE std::for_each ( data.begin(), data.end(), boost::bind( &print , boost::bind( &string_ptr_t::get , boost::bind::_1 ))); return 0; } On 5/20/07, Ovanes Markarian <om_boost@keywallet.com> wrote:

Christian,

Can you please specify what happens when the compiler crashes? There is a known issue that template intensive code can crash the VC compiler, to resolve it, you can increase the memory heap size used by VC internally. You may read more on it at:

http://www.boost.org/doc/html/variant/misc.html#variant.troubleshooting

This is not only boost::variant issue and can happen in other libraries as well.

Best Regards, Ovanes

-----Ursprüngliche Nachricht----- Von: Christian Henning [mailto:chhenning@gmail.com] Gesendet: Sonntag, 20. Mai 2007 00:41 An: boost-users@lists.boost.org Betreff: Re: [Boost-users] Converting loop to using boost::lambda where containers has boost::shared_ptrs

...

I am glad to know I still the have skill of breaking compilers. :)

Well, I seem to have similar skills. The code below crashes my compiler ( VC7.1 SP 1), as well.

void print( const std::string& s ) { std::cout << s; }

int main ( int, char** ) { typedef boost::shared_ptr<A> A_ptr_t; typedef boost::shared_ptr<D> D_ptr_t;

typedef std::vector < boost::shared_ptr<Base> > Data_t; Data_t m_data;

A_ptr_t a ( new A ( 50 ) ); D_ptr_t d ( new D ( 30 ) );

m_data.push_back ( a ); m_data.push_back ( d );

boost::uint32_t indent_value = 4;

// this works boost::bind( &print , boost::bind( &Base::to_String , A_ptr_t( new A( 5 ) ) , indent_value ))();

// this doesn't work - ICE std::for_each ( m_data.begin(), m_data.end(), boost::bind( &print , boost::bind( &Base::to_String , boost::bind::_1 , indent_value )));

return 0; }

I know this is not the solution. I'm still using a seperate function print() for outputting. I will keep trying to solve that one.

On the other hand it would be nice if boost::bind comes some handy function like the print(). Just a thought.

Christian _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Thanks a lot, again. ;-) This is the working code now. #include <string> #include <sstream> #include <boost/cstdint.hpp> #include <vector> #include <boost/shared_ptr.hpp> #include <boost/bind.hpp> #include <iostream> class Base { public: virtual std::string to_String ( boost::uint32_t indent ) = 0; }; class A : public Base { public: A ( boost::uint32_t value ) : m_value ( value ) {} virtual std::string to_String ( boost::uint32_t indent ) { std::stringstream output; for ( boost::uint32_t i = 0; i < indent; i++ ) { output << " "; } output << m_value; return output.str(); } private: boost::uint32_t m_value; }; class D : public Base { public: D ( boost::uint32_t value ) : m_value ( value ) {} virtual std::string to_String ( boost::uint32_t indent ) { std::stringstream output; for ( boost::uint32_t i = 0; i < indent; i++ ) { output << " "; } output << m_value; return output.str(); } private: boost::uint32_t m_value; }; void print( const std::string& s ) { std::cout << s; } int main ( int, char** ) { typedef boost::shared_ptr<A> A_ptr_t; typedef boost::shared_ptr<D> D_ptr_t; typedef std::vector < boost::shared_ptr<Base> > Data_t; Data_t m_data; A_ptr_t a ( new A ( 50 ) ); D_ptr_t d ( new D ( 30 ) ); m_data.push_back ( a ); m_data.push_back ( d ); boost::uint32_t indent_value = 4; std::for_each ( m_data.begin(), m_data.end(), boost::bind( &print , boost::bind( &Base::to_String , _1 , indent_value ))); return 0; } It's still not quite what we what but we are getting closer. ;-) Christian

Thanks Roman. Will do. On 5/21/07, Roman Perepelitsa <roman.perepelitsa@db.com> wrote:

Christian Henning <chhenning <at> gmail.com> writes:

...

Thanks a lot, again.

This is the working code now. [cut]

You can use transform + ostream_iterator instead of for_each + print.

transform( m_data.begin() , m_data.end() , ostream_iterator<string>(cout, "\n") , boost::bind( &Base::to_String , _1 , indent_value));

And instead of handcrafted loop for indentation you can use constructor of std::string.

virtual string to_String ( boost::uint32_t indent ) { stringstream output; output << string(indent, ' ') << m_value; return output.str(); }

Roman Perepelitsa.

_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Alright, I solved it. Two small changes in the code did it. Hope they are not too bad for you. First I needed to remove the =0 statement for the to_string in your base class. If I don't do that I can the following error: c:\boost_1_34_0\boost\tuple\detail\tuple_basic.hpp(328) : error C2259: 'Base' : cannot instantiate abstract class [snip] So my base class looks like as follows: class Base { public: virtual std::string to_String ( boost::uint32_t indent ) { return "" ;} }; Second change was to remove the boost::bind lib and to use lambda's bind. I also needed to add an asterisk to _1. Here is the complete code that works on my machine. #include <string> #include <sstream> #include <boost/cstdint.hpp> #include <vector> #include <boost/shared_ptr.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> #include <iostream> using namespace boost::lambda; class Base { public: virtual std::string to_String ( boost::uint32_t indent ) { return "" ;} }; class A : public Base { public: A ( boost::uint32_t value ) : m_value ( value ) {} virtual std::string to_String ( boost::uint32_t indent ) { std::stringstream output; for ( boost::uint32_t i = 0; i < indent; i++ ) { output << " "; } output << m_value; return output.str(); } private: boost::uint32_t m_value; }; class D : public Base { public: D ( boost::uint32_t value ) : m_value ( value ) {} virtual std::string to_String ( boost::uint32_t indent ) { std::stringstream output; for ( boost::uint32_t i = 0; i < indent; i++ ) { output << " "; } output << m_value; return output.str(); } private: boost::uint32_t m_value; }; const char* print( const std::string& s ) { return s.c_str(); } int main ( int, char** ) { typedef boost::shared_ptr<A> A_ptr_t; typedef boost::shared_ptr<D> D_ptr_t; typedef std::vector < boost::shared_ptr<Base> > Data_t; Data_t m_data; A_ptr_t a ( new A ( 50 ) ); D_ptr_t d ( new D ( 30 ) ); m_data.push_back ( a ); m_data.push_back ( d ); boost::uint32_t indent_value = 4; std::for_each ( m_data.begin(), m_data.end(), std::cout << bind( &Base::to_String, *_1, indent_value ) ); return 0; } Regards, Christian

On Sat, 2007-05-19 at 16:23 +0100, Stuart Dootson wrote:

...

Its close but not quite. I get an error message that _1 is ambiguous

Append_Frame.cpp:48: error: reference to '_1' is ambiguous /usr/include/boost/lambda/core.hpp:69: error: candidates are: const boost::lambda::placeholder1_type& boost::lambda::<unnamed>::_1 /usr/include/boost/bind/placeholders.hpp:54: error: boost::arg<1> <unnamed>::_1

Stephen

Nat's using Boost.Bind, not the bind in Boost.Lambda - they both define _1 as a placeholder, so they clash...

Using bind from Boost.Lambda, you'll need nested binds to cope with shared_ptr:

using namespace boost::lambda; std::for_each(m_data.begin(), m_data.end(), output << bind(&Verification_Type_Info::to_String, bind(boost::shared_ptr<Verification_Type_Info>::get, _1), new_indent_limit));

I think we are closer. Append_Frame.cpp: In member function 'virtual std::string libreverse::java_module::Append_Frame::to_String(uint32_t) const': Append_Frame.cpp:50: error: invalid use of non-static member function 'T* boost::shared_ptr<T>::get() const [with T = libreverse::java_module::Verification_Type_Info]' make[6]: *** [libio_java_class_la-Append_Frame.lo] Error 1 I am not sure the second bind is doing what you wanted. Stephen