Robert Jones schrieb:

On Thu, Oct 2, 2008 at 11:12 AM, Peter Barker <newbarker@gmail.com> wrote:

...

Hello,

Here's an example of my problem:

#include <algorithm> #include <vector>

#include <boost/bind.hpp>

class TheClass { };

void accept(TheClass& tc) { }

int main() { std::vector<TheClass*> cont;

// Compile error - how to dereference _1 ??? std::for_each(cont.begin(),cont.end(),boost::bind(&accept,_1)); }

How can I dereference _1 so I can use the accept function?

#include <algorithm> #include <vector>

#include <boost/lambda/bind.hpp> #include <boost/lambda/lambda.hpp>

class TheClass { };

void accept(TheClass& tc) { }

int main() { using namespace boost; using namespace boost::lambda;

std::vector<TheClass*> cont;

// Compile error - how to dereference _1 ??? std::for_each(cont.begin(),cont.end(),bind(accept,*_1)); }

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

Hi Rob, with std::for_each(cont.begin(),cont.end(),bind(&accept,*_1)); you can dereference _1. Best regards Franz

On Thu, Oct 2, 2008 at 11:39 AM, Robert Jones <robertgbjones@gmail.com> wrote:

On Thu, Oct 2, 2008 at 11:12 AM, Peter Barker <newbarker@gmail.com> wrote:

...

Hello,

Here's an example of my problem:

#include <algorithm> #include <vector>

#include <boost/bind.hpp>

class TheClass { };

void accept(TheClass& tc) { }

int main() { std::vector<TheClass*> cont;

// Compile error - how to dereference _1 ??? std::for_each(cont.begin(),cont.end(),boost::bind(&accept,_1)); }

How can I dereference _1 so I can use the accept function?

#include <algorithm> #include <vector>

#include <boost/lambda/bind.hpp> #include <boost/lambda/lambda.hpp>

class TheClass { };

void accept(TheClass& tc) { }

int main() { using namespace boost; using namespace boost::lambda;

std::vector<TheClass*> cont;

// Compile error - how to dereference _1 ??? std::for_each(cont.begin(),cont.end(),bind(accept,*_1)); }

Rob, Thanks for the suggestion - my sample program was actually too stripped down. TheClass is a base with pure virtual methods and your suggestion gives me the "cannot instantiate abstract class" compiler error. Here's a new sample program: #include <algorithm> #include <vector> #include <boost/lambda/bind.hpp> #include <boost/lambda/lambda.hpp> class TheClass { public: virtual ~TheClass() {} virtual void pvm() = 0; }; class DerivedClass : public TheClass { void pvm() {} }; void accept(TheClass& tc) { } int main() { std::vector<TheClass*> cont; using namespace boost::lambda; using boost::lambda::_1; // Compile error - cannot instantiate abstract class - how to dereference _1 ??? std::for_each(cont.begin(),cont.end(),bind(&accept,*_1)); }

On Thu, 2 Oct 2008 14:36:01 +0100 "Peter Barker" <newbarker@gmail.com> wrote:

On Thu, Oct 2, 2008 at 11:45 AM, Sven Gaerner <sgaerner@gmx.net> wrote:

...

On Thu, 2 Oct 2008 11:12:54 +0100 "Peter Barker" <newbarker@gmail.com> wrote:

...

Hello,

Here's an example of my problem:

#include <algorithm> #include <vector>

#include <boost/bind.hpp>

class TheClass { };

void accept(TheClass& tc) { }

int main() { std::vector<TheClass*> cont;

// Compile error - how to dereference _1 ??? std::for_each(cont.begin(),cont.end(),boost::bind(&accept,_1)); }

How can I dereference _1 so I can use the accept function?

Regards,

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

You don't have to dereference _1. Your accept function must look like this: void accept(TheClass *arg) { } Your std::vector contains pointers to TheClass so std::for_each() passes objects of that type to your functor, in this case a pointer to types of TheClass.

Sven,

I was trying to avoid changing the signature of accept as it has other call sites and I would need to update them. It's what I did in the end though. Thanks,

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

Peter, I didn't think about avoiding to change the signature. Sorry for that. What about using a specific delegate functor? Somethink like that: struct Delegate { void operator()(TheClass *arg) { accept(*arg); } }; And then pass this functor to std::for_each(); std::for_each(cont.begin(),cont.end(), Delegate()); That wouldn't break the signature of the accept function, but it depends on that particular implementation. Sven

On Thu, Oct 2, 2008 at 3:25 PM, Peter Dimov <pdimov@pdimov.com> wrote:

Peter Barker: ...

...

void accept(TheClass& tc) { }

int main() { std::vector<TheClass*> cont;

// Compile error - how to dereference _1 ??? std::for_each(cont.begin(),cont.end(),boost::bind(&accept,_1)); }

How can I dereference _1 so I can use the accept function?

With boost::bind, there's no easy way to dereference _1. You'd need

template<class T> T& deref( T* p ) { return *p; }

std::for_each( cont.begin(), cont.end(), boost::bind( accept, boost::bind( deref<TheClass>, _1 ) ) ); Peter,

It's nice to hear the answer from the horses mouth (so to speak)! Regards, Pete