[lambda]How can I call function of objects in std::list while using std::for_each?
Please help me! I want to call a virtual function of objects in std::list while using std::for_each: struct DiscardableItem { void Discard() { std::cout<<"Discard item!"<<std::endl; } }; std::list<DiscardableItem*> items; items.push_back(new DiscardableItem); items.push_back(new DiscardableItem); std::for_each( items.rbegin(), items.rend(), _1->*&DiscardableItem::Discard ); But DiscardableItem::Discard does not be called. How can I make it work? thanks! I think lambda can solve this problem easily.
But DiscardableItem::Discard does not be called. How can I make it work? thanks! I think lambda can solve this problem easily.
You don't need boost::lambda here, you can easily solve this with boost::bind std::for_each( items.rbegin(), items.rend(), boost::bind(&DiscardableItem::Discard, _1) ); If you *want* to use boost::lambda I'm sure someone else will help :) Regards, Alex
I am sorry that I did not figure out the whole intention. Beside calling member function, I hope to delete the object immediately. I wrote the code at first time: std::for_each( items.rbegin(), items.rend(), (_1->*&DiscardableItem::Discard, bind(delete_ptr(), _1)) ); after for_each, objects deleted, but Discard function did not been called. If using Bind can do the same thing, please tell me. thanks! 2009/3/23 Alex MDC <alex.mdc@gmail.com>
But DiscardableItem::Discard does not be called. How can I make it work?
thanks! I think lambda can solve this problem easily.
You don't need boost::lambda here, you can easily solve this with boost::bind
std::for_each( items.rbegin(), items.rend(), boost::bind(&DiscardableItem::Discard, _1) );
If you *want* to use boost::lambda I'm sure someone else will help :)
Regards, Alex
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On Sun, Mar 22, 2009 at 8:52 PM, 钱晓明 <kyleqian@gmail.com> wrote:
I am sorry that I did not figure out the whole intention. Beside calling member function, I hope to delete the object immediately. I wrote the code at first time:
std::for_each( items.rbegin(), items.rend(), (_1->*&DiscardableItem::Discard, bind(delete_ptr(), _1)) );
after for_each, objects deleted, but Discard function did not been called. If using Bind can do the same thing, please tell me. thanks! 2009/3/23 Alex MDC <alex.mdc@gmail.com>
At this point, though you probably *can* do what you want with bind, you may want to consider if it will be easier (and clearer in intent) to simple write a function object that implements your desired behavior: struct Discarder : std::unary_function<DiscardableItem*,void> { void operator()( DiscardableItem * pd ) const { pd->Discard(); delete pd; } }; std::for_each( items.rbegin(), items.rend(), Discarder() ); HTH, Christopher
I think that your advice is a good choice. Using a function object is more clearly. However, if some one know how to do this using Lambda or Bind, please tell me. I want to know it. thanks! 2009/3/23 Christopher Currie <christopher@currie.com>
On Sun, Mar 22, 2009 at 8:52 PM, 钱晓明 <kyleqian@gmail.com> wrote:
I am sorry that I did not figure out the whole intention. Beside calling member function, I hope to delete the object immediately. I wrote the code at first time:
std::for_each( items.rbegin(), items.rend(), (_1->*&DiscardableItem::Discard, bind(delete_ptr(), _1)) );
after for_each, objects deleted, but Discard function did not been called. If using Bind can do the same thing, please tell me. thanks! 2009/3/23 Alex MDC <alex.mdc@gmail.com>
At this point, though you probably *can* do what you want with bind, you may want to consider if it will be easier (and clearer in intent) to simple write a function object that implements your desired behavior:
struct Discarder : std::unary_function<DiscardableItem*,void> { void operator()( DiscardableItem * pd ) const { pd->Discard(); delete pd; } };
std::for_each( items.rbegin(), items.rend(), Discarder() );
HTH, Christopher _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
钱晓明:
However, if some one know how to do this using Lambda or Bind, please tell me. I want to know it. thanks!
You can use one of (_1->*&DiscardableItem::Discard)() bind(&DiscardableItem::Discard, _1)
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钱晓明