Re: [Boost-users] Lambda and placeholders

Subject: Re: [Boost-users] Lambda and placeholders
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2012-04-02 07:12:30

On 04/02/2012 09:52 AM, Sven Bauhan wrote:
>> namespace ll = boost::lambda;
>> ... = std::find_if(..., ll::bind(&Timeslice::contains,
>>   ll::bind(&LightningSlice::timeslice, ll::_1), time_));
>>
>> Yes, it's ugly. Unfortunately, you can't really improve on it.
>>
>> Sebastian
>> _______________________________________________
> Thanks,
>
> I tried this suggestion:
>
> #include<boost/lambda/bind.hpp>
> namespace ll = boost::lambda;
>
> 	LightningQueue::const_iterator l
> 		= std::find_if( m_lightnings.begin(), m_lightnings.end(),
> 				bind(&boost::posix_time::time_period::contains, 		
> 				ll::bind(&LightningSlice::timeslice, ll::_1 ), time_ 	
> 			) );
>
> But then I got this error message:
>
> ../LightningIndex.cpp: In member function 'weather::LightningSlice
> weather::LightningIndex::getLightningSlice(boost::posix_time::ptime)':
> ../LightningIndex.cpp:40: error: no matching function for call to
> 'bind(<unresolved overloaded function type>, const
> boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<2,
> boost::lambda::function_action<2, boost::lambda::detail::unspecified>  >,
> boost::tuples::tuple<const boost::posix_time::time_period&
> (weather::LightningSlice::* const)()const, const
> boost::lambda::lambda_functor<boost::lambda::placeholder<1>  >,
> boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type,
> boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type,
> boost::tuples::null_type, boost::tuples::null_type>  >  >,
> boost::posix_time::ptime&)'
>
> This is even more confusion than the first error message.
The problem is that boost::posix_time::time_period::contains is 
overloaded. Thus the compiler can not decide which function address you 
mean.
The solution I usually go with is the following:

bool (boost::posix_time::time_period::*f)(boost::posix_time::time_period 
const &) const = &boost::posix_time::time_period::contains;

or:

bool (boost::posix_time::time_period::*f)(boost::posix_time::ptime const 
&) const = &boost::posix_time::time_period::contains;

Depending on what type time_ actually is ...

and then continue with:

LightningQueue::const_iterator l
                = std::find_if( m_lightnings.begin(), m_lightnings.end(),
                                bind(f, 		
                                ll::bind(&LightningSlice::timeslice, ll::_1 ), time_ 	
                        ) );

> Greetings, Sven
> _______________________________________________
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