Re: [boost] [Bind] How do I get bind to deduce the return type offor_each?

Subject: Re: [boost] [Bind] How do I get bind to deduce the return type offor_each?
From: Thomas Jordan (thomasjordan_at_[hidden])
Date: 2010-04-19 14:48:16

Thomas Jordan wrote: 
> Thanks a lot for the suggestion, I did take a look at Lambda library, and 
> I saw that it used some extra type information in its STL 
> algorithm wrappers (the 'sig') to help it figure out the return types. 
> However, I am against using the Lambda library 
> for other reasons, I only want to use the bind library. I'd appreciate 
> some specific advice on how to get the type deduction 
> with the Boost.bind library. Or is this just not possible with 
> Boost.bind? 

Peter Dimov replied:

-----------------

It's not. Boost.Bind only supports function objects with a specific, fixed 
type. There is no mechanism to tell it that the return type of 

struct myForEach 
{ 
   template <typename II, typename F> 
   F operator()(II begin, II end, F function) const 
   { 
      return std::for_each(begin, end, function); 
   } 
}; 

is the same as its third argument. In this specific case I'd just use 

struct myForEach 
{ 
   typedef void result_type; 
   template <typename II, typename F> 
   void operator()(II begin, II end, F function) const 
   { 
      std::for_each(begin, end, function); 
   } 
}; 

--------------------

Thanks, Peter, and thanks to everyone else who replied, for their helpful suggestions.  

FWIW, I'm putting together a presentation for my colleagues, to show the facilities for higher-order programming in STL and Boost, and I wanted to show a couple of 'out-there' examples to illustrate their power.  I'm a bit of an arriviste and my C++ is 'improving,' but I'm really impressed that you can do functional-style programming so nicely in C++.

Regards, Tom.