Re: [Boost-users] [lambda] Does Boost.Lambda support localvariables?

Subject: Re: [Boost-users] [lambda] Does Boost.Lambda support localvariables?
From: Peter Dimov (pdimov_at_[hidden])
Date: 2009-01-13 08:27:17

Robert Jones:
> I guess I could write something like
>
> boost::function< bool( int ) > exceed_detail = _1 > max || _1 < min;
> boost::function< bool( size_t, size_t ) > exceeds_range = bind(
> exceeds_detail, bind( element, _1, _2 ) );
>
> but it seems to introduce additional arbitrary artifacts which is not 
> ideal,
> and obscures the logic to my mind.

I admit that the workarounds aren't pretty. In this case you could've 
written

exceeds_range = bind( protect( _1 > max || _1 < min ), bind( element, _1, 
_2 ) );

The protect is needed because lambda::bind evaluates its first argument 
(boost::bind does not).

In general you can introduce a local _3 via:

exceeds_range_impl = ( _3 = bind( element, _1, _2 ), _3 > max || _3 < min );
exceeds_range = boost::bind( exceeds_range_impl, _1, _2, 0 );

but... one'd rather write the function by hand and be done with it. :-)