simple boost::bind question
Hello all: Hoping someone might help with a simple problem; how I might call a member on a boost::bind placeholder, see below ... #include <list> class Xtype { public: Xtype(int v) : value_(v) { } int the_value() const { return this->value_; } private: int value_; }; template <typename Predicate> class Excise { public: void operator()(std::list<Xtype>& li) const { li.remove_if(boost::bind(Predicate(), ::_1, 10)); } }; ... what I really want is something more like [, note the call of Xtype::this_value() ]: void operator()(std::list<Xtype>& li) const { li.remove_if(boost::bind(Predicate(), ::_1.the_value(), 10)); } But how do I achieve that (, if at all possible); as seemingly ::_1.the_value() is illegal/invalid code ? Thanks in advance, -- Manfred
Replying to my own post here, apologies all, what was I thinking ::_1 is just a place holder. However, I'd much like to achieve something along similar lines .. all help appreciated. -- Manfred Manfred Doudar wrote:
Hello all:
Hoping someone might help with a simple problem; how I might call a member on a boost::bind placeholder, see below ...
#include <list>
class Xtype { public:
Xtype(int v) : value_(v) { }
int the_value() const { return this->value_; }
private:
int value_; };
template <typename Predicate> class Excise { public:
void operator()(std::list<Xtype>& li) const { li.remove_if(boost::bind(Predicate(), ::_1, 10)); } };
... what I really want is something more like [, note the call of Xtype::this_value() ]:
void operator()(std::list<Xtype>& li) const { li.remove_if(boost::bind(Predicate(), ::_1.the_value(), 10)); }
But how do I achieve that (, if at all possible); as seemingly ::_1.the_value() is illegal/invalid code ?
Thanks in advance,
Manfred Doudar <manfred.doudar <at> rsise.anu.edu.au> writes:
template <typename Predicate> class Excise { public:
void operator()(std::list<Xtype>& li) const { li.remove_if(boost::bind(Predicate(), ::_1, 10)); } };
Hello. Try this: bind(Predicate(), bind(&Xtype::the_value, _1), 10) HTH, Roman Perepelitsa
Roman Perepelitsa wrote:
Try this: bind(Predicate(), bind(&Xtype::the_value, _1), 10)
Thank you kindly Roman, that helped - and is obvious now that I see it, again many thanks. I do however have one more boost::bind question that I can't quite get myself around. I want replace the following for-loop with a call to std::for_each, and am near certain that bind would do it: std::list<boost::tuple<int, float, std::string> > li; ... for (std::list<boost::tuple<int, float, std::string> >::iterator it = li.begin(); it != li.end(); ++it) { // this is ok - is all part of a class that inherits from MyFunctor MyFunctor::operator()(boost::get<0> (*it)); } How might I convert the above to something using std::for_each, and boost::bind? Again, with thanks in advance -- Manfred
Manfred Doudar <manfred.doudar <at> rsise.anu.edu.au> writes:
Thank you kindly Roman, that helped - and is obvious now that I see it, again many thanks.
I do however have one more boost::bind question that I can't quite get myself around.
I want replace the following for-loop with a call to std::for_each, and am near certain that bind would do it:
std::list<boost::tuple<int, float, std::string> > li;
...
for (std::list<boost::tuple<int, float, std::string> >::iterator it = li.begin(); it != li.end(); ++it) { // this is ok - is all part of a class that inherits from MyFunctor
MyFunctor::operator()(boost::get<0> (*it)); }
How might I convert the above to something using std::for_each, and boost::bind?
Again, with thanks in advance
Hi. It is almost imposible to explicitly bind boost::get because it's an overloaded name with huge signature. The best thing you can do is to write your own functor which can deduce tuple element type. Here is how you do it. #include <list> #include <algorithm> #include <iostream> #include <boost/lambda/bind.hpp> #include <boost/tuple/tuple.hpp> #include <boost/mpl/if.hpp> #include <boost/type_traits/is_const.hpp> using namespace boost; using namespace boost::lambda; using namespace std; template <int N> struct tuple_get { template <class T> struct sig { typedef typename tuples::element< N, typename tuples::element<1, T>::type >::type ret; typedef typename mpl::if_< is_const<typename tuples::element<1, T>::type>, typename tuples::access_traits<ret>::const_type, typename tuples::access_traits<ret>::non_const_type >::type type; }; template <class T> typename sig<tuple<tuple_get, const T> >::type operator()(const T & t) const { return t.template get<N>(); } template <class T> typename sig<tuple<tuple_get, T> >::type operator()(T & t) const { return t.template get<N>(); } }; void print(int i) { cout << i << endl; } int main() { typedef boost::tuple<int, float, std::string> data; typedef list<data> data_list; data_list li; std::for_each( li.begin(), li.end(), bind(print, bind(tuple_get<0>(), _1))); } This code uses boost::lambda::bind instead of boost::bind because I don't know how to specify return type for functor in terms of boost::bind. 'typedef ... result_type' is not enough here because return type depends of argument type. Check boost::bind documentation if you want to use it instead of boost::lambda::bind. Roman Perepelitsa.
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Roman Perepelitsa