RE: [boost] Function and Bind

From: David Brownell (brownell_at_[hidden])
Date: 2001-10-15 17:33:57

Thanks for your help, that got me over my hurdle!

-----Original Message-----
From: Wilka [mailto:wilka_at_[hidden]] 
Sent: Monday, October 15, 2001 1:57 PM
To: boost_at_[hidden]
Subject: RE: [boost] Function and Bind

When you're passing a functor (such as boost::function) to a
boost::function, you need to explicitly tell it what the return value is. So
in your case, if you change:

<code>
//BEGIN PROBLEM
OneArgFunction          f_oneArg;

f_oneArg = boost::bind(f2, ulValue, _1);
//END PROBLEM
return(DoIt_One(f_oneArg));
</code>

To

<code>
//BEGIN PROBLEM
OneArgFunction          f_oneArg;

f_oneArg = boost::bind<bool>(f2, ulValue, _1); // Note the "<bool>" //END
PROBLEM return(DoIt_One(f_oneArg)); </code>

It should work fine.

- Wilka 

> -----Original Message-----
> From: brownell_at_[hidden] [mailto:brownell_at_[hidden]]
> Sent: 15 October 2001 21:15
> To: boost_at_[hidden]
> Subject: [boost] Function and Bind
> 
> 
> I have a question that is probably better asked in code than in
> words, but I will try the words route first, and if that doesn't 
> work, I have pasted code that may explain the situation better.
> 
> I have one function that takes 1 arg (call it Func1), another that
> takes 2 args (call it Func2).  Both these functions take 
> boost::functionX params.  Somehow, I need to bind a value to the 
> first arg in Func2, and pass that new function to Func1.  
> 
> I can not wait for the return value of Func1, as these function are
> used to update algorithm progress.
> 
> Make any sense?  Hopefully the code will.
> 
> Thanks for any and all help,
> Dave Brownell
> 
> #include<iostream>
> 
> #include "boost\bind.hpp"
> #include "boost\Function.hpp"
> 
> typedef boost::function1<bool, unsigned long>                       
> OneArgFunction;
> typedef boost::function2<bool, unsigned long, unsigned long>        
> TwoArgFunction;
> 
> inline bool WriteOne(unsigned long ul1)
> {
>     std::cout << ul1 << std::endl;
>     return(true);
> }
> 
> inline bool WriteTwo(unsigned long ul1, unsigned long ul2)
> {
>     std::cout << "(" << ul2 << ") " << ul1 << std::endl;
>     return(true);
> }
> 
> bool DoIt_One(OneArgFunction &f)
> {
>     if(f.empty() == false)
>         f(1);
> 
>     return(true);
> }
> 
> bool DoIt_Two(TwoArgFunction &f2, unsigned long ulValue)
> {
>     if(f.empty() == false)
>         return(false);
> 
>     //BEGIN PROBLEM
>     OneArgFunction          f_oneArg;
> 
>     f_oneArg = boost::bind(f2, ulValue, _1);
>     //END PROBLEM
>     return(DoIt_One(f_oneArg));
> }
> 
> int main(void)
> {
>     TwoArgFunction          f2 = &WriteTwo;
> 
>     DoIt_Two(f2, 2);
> 
>     return(true);
> }
> 
> 
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