RE: [Boost-Users] bind: I just keep trying...

From: Tom Matelich (tmatelich_at_[hidden])
Date: 2002-09-26 10:40:31

I think the best solution for you would be to put boost::function<short>'s
in your map.  Look at the example in the bind documentation at
http://www.boost.org/libs/bind/bind.html#with_boost_function

Tom

> -----Original Message-----
> From: dick.bridges_at_[hidden] [mailto:dick.bridges_at_[hidden]]
> Sent: Thursday, September 26, 2002 7:57 AM
> To: Boost-Users_at_[hidden]
> Subject: RE: [Boost-Users] bind: I just keep trying...
> 
> 
> 
> I'm trying to store member function pointers.  For purposes of this
> discussion, the key is an int.
> 
> <context>
> X is the virtual base class for polymorphic message classes.
>       all messages have a session-d attribute
> 
> Ys are instances of classes derived from a virtual message hanler base
> class.
>       foo() is the message handler function.
> 
> Z is the 'message pump' that dispatches messages to Ys based upon the
> session-id.
> 
> Y instances insert make_pair(session-id, message_handler) 
> pairs into the
> map.
>       (I think _1 is 'this' during the insert.)
> 
> Z calls the Y instance message-handler  using the session-id 
> key to the
> map.
> </context>
> 
> 
> 
>                                                               
>                                                               
>           
>                       Mark Storer                             
>                                                               
>           
>                       <mstorer_at_cardiff         To:      
> "'Boost-Users_at_[hidden]'" <Boost-Users_at_[hidden]> 
>                 
>                       .com>                    cc:            
>                                                               
>           
>                                                Subject: RE: 
> [Boost-Users] bind:  I just keep trying...                    
>             
>                       09/25/2002 04:47                        
>                                                               
>           
>                       PM                                      
>                                                               
>           
>                       Please respond                          
>                                                               
>           
>                       to Boost-Users                          
>                                                               
>           
>                                                               
>                                                               
>           
>                                                               
>                                                               
>           
> 
> 
> 
> 
> I'm a little confused as to what you're aiming for here... a 
> map of ints to
> function pointers (that can point to Y::foo)?
> 
> This should do the trick, provided I'm recalling my function pointer
> declarations correctly
> std::map<int, short()(*X)>
> 
> Further boost::bind creates an INSTANCE of a functor.  Giving 
> the compiler
> an instance when it wants a type is not a good way to keep it happy.
> 
> Now if what you're actually after is calling Y::foo on a 
> colleciton of Y's,
> then you don't need a collection of function pointers for 
> each instance in
> the first place, which is where bind comes in.  According to my flimsy
> understanding of bind (I haven't used it yet), this should do 
> the trick:
> 
> X someX;
> std::vector<Y> &wise = BuildYs();  // wise == plural of Y
> 
> std::for_each(
>   wise.begin(),
>   wise.end(),
>   boost::bind<short>(&Y::foo, &someX)
> );
> 
> If you want the X parameter to vary from one call of foo to 
> the next, I
> suggest rolling your own loop... or incorporating the X* into 
> Y, at which
> point you can get rid of the X* parameter, and use 
> boost::bind(&Y::foo), or
> std::mem_fun(&Y::foo).
> 
> --Mark Storer
>   Software Engineer
>   Cardiff Software
> 
> #include <disclaimer>
> typedef std::disclaimer<Cardiff> Discard;
> 
> 
> -----Original Message-----
> From: dick.bridges_at_[hidden] [mailto:dick.bridges_at_[hidden]]
> Sent: Wednesday, September 25, 2002 4:08 PM
> To: boost-users_at_[hidden]
> Subject: [Boost-Users] bind: I just keep trying...
> 
> 
> Everytime I think I have a clue, I'm reminded how little I REALLY
> understand.
> 
> <error compiler='VC6SP4'>
> 'map' : invalid template argument for '_Ty', type expected
> </error>
> 
> <snippet>
> struct X
> {
> }
> 
> struct Y
> {
>       short foo(X*);
> }
> 
> struct Z
> {
>       map<int, bind(&Y::foo, _1, _2) > myMap;
> }
> </snippet>
> 
> I thought I saw how to do this somewhere on the website but I 
> sure can't
> find it now.  Any help GREATFULLY appreciated.
> 
> 
> 
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