Re: [Boost-users] Phoenix lazy functions

From: Joel de Guzman (joel_at_[hidden])
Date: 2005-07-18 23:25:25

Edson Tadeu wrote:
> I'm trying to learn to use Phoenix, but I haven't found an example of
> how to do the following simple thing using its inline lazy function
> creation (it seems that there isn't a simple way to do this):
> 
> struct Test {
>   int x;
>   void Test() {x = 1;}
>   void inc(int i) { x += i; }
> };
> 
> void main() {
>   vector<Test> v;
>   v.resize(5);
>   
>   // v == {1, 1, 1, 1, 1}
> 
>   for_each(v.begin(), v.end(), arg1.inc(1 + arg1.x) )
> 
>   // v == {3, 3, 3, 3, 3}
> }
> 
> 
> The only ways I found to do this involves function<> that needs an
> external functor declaration, but this is ugly just like old STL
> functors, or using member_function_ptr and member_var_ptr templates,
> but I couldn't get them to work on Borland C++.
> 
> Anyone knows how to do it, keeping simplicity and elegance?

Bind is your friend:

     for_each(v.begin(), v.end(),
         bind(&Test::inc, arg1, 1 + bind(&Test::x, arg1));

This syntax assumes Phoenix-2. Alas, Borland is no longer
supported. I guess your only option now is to use boost::bind.
The syntax should be the same, except that arg1 is _1.

Regards,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net