Re: [boost] [lambda] Binding to templated functions

From: Robert Jones (robertgbjones_at_[hidden])
Date: 2008-07-22 08:01:11

On Tue, Jul 22, 2008 at 12:28 PM, Mathias Gaunard <
mathias.gaunard_at_[hidden]> wrote:

> Robert Jones wrote:
> >   typedef pair<int, S *> Pair;
> >   vector<Pair> pairs;
> >   bool trueForAll = ( find_if( _1, _2, _3 ) == _2 )(
> >       pairs.begin( ),
> >       pairs.end( ),
> >       ! bind( & S :: predOfS, bind( & Pair :: second, _1 ) ) );
> > }
> >
> > The last line gives me compile errors.
> >
> > Two things:
> > - I think I need to specicy the template parameters to find_if, but I'm
> not
> > sure quite what they are!
>
> Why are you even doing this?
> find_if(pairs.begin(), pairs.end(), your_lambda_expression) is sufficient.
>
> Otherwise, it is more practical to use a lazy function. Phoenix is
> better for that, and it actually already provides lazy versions of
> standard algorithms.
>
>
> > - The error message reckons the last arg to find_if is placeholder<4>,
> not
> > placeholder<3>, why?
>
> Because _1 is placeholder<0>.
>

Hi Mathias

I can entirely understand your horror at this code, and indeed it is highly
contrived
to be about the simplest thing I can construct which reproduces the symptoms
produced from the real code.

The essential feature, in the terms of my example code, is that I only want
to
evaluate the end( ) method once, and avoid placing it in a named variable.

It seems Phoenix may be the answer to my needs, so many thanks for that
tip.

Regards, Rob.