Re: [Boost-users] [signals] maximum combiner example calls slot twice

Subject: Re: [Boost-users] [signals] maximum combiner example calls slot twice
From: Frank Mori Hess (fmhess_at_[hidden])
Date: 2009-04-24 13:41:41

On Friday 24 April 2009, Dominique Devienne wrote:
> In http://www.boost.org/doc/libs/1_38_0/doc/html/signals/tutorial.html,
> once I read:
>
>   "The input iterators passed to the combiner transform dereference
> operations into slot calls"
>
> I realized that the maximum<T> combiner introduced earlier is
> implemented using:
>
>       if (max_value < *first)
>         max_value = *first;
>
> Which ends up calling the slot twice. 

Dereferencing a slot call iterator multiple times only runs the slot once.  
After that, it returns a cached copy of the return value.