Re: [boost] Re: more lambda woes

From: Jaakko Jarvi (jajarvi_at_[hidden])
Date: 2004-03-09 13:24:24

On Mar 9, 2004, at 12:17 PM, David Abrahams wrote:

> Jaakko Jarvi <jajarvi_at_[hidden]> writes:
>
>> On Mar 9, 2004, at 11:18 AM, David Abrahams wrote:
>>
>>>
>>> Lambda docs say:
>>>
>>>        "When an actual argument is supplied for a placeholder, the
>>>         parameter passing mode is always by reference"
>>>
>>> Yet when I changed the following code from using boost::bind to
>>> boost::lambda, I got complaints that Field is an abstract class and
>>> can't be copied.
>>>
>>>     void (self_t::* insert_)(Field const&) = &self_t::insert;
>>>     std::for_each(fields.begin(), fiends.end(), bind(insert_, this,
>>> _1));
>>>
>>> What gives?
>>>
>>

This requires a bigger fix.
BLL uses tuples to manipulate type sequences that are being used in 
type deduction.
In this process, a tuple type containing a non-reference abstract type 
is formed.
Such an object is never instantiated, but it seems that just declaring 
such a type
is not allowed.

So the fix is to ditch tuples there, and move to type sequences, which 
requires
quite some coding.

Is_abstract may give a quick fix.

   Jaakko

>> Can you post (email directly) a full example. I couldn't immediately
>> get similar
>> code to fail.
>
>   #include <boost/lambda/lambda.hpp>
>   #include <boost/lambda/bind.hpp>
>
>   using namespace boost::lambda;
>
>   struct X
>   {
>       virtual void f() = 0;
>   };
>
>   struct Y : X
>   {
>       void f() {};
>   };
>
>   struct Z
>   {
>       void g(X const& x)
>       {
>       }
>
>       void h(X const& x)
>       {
>           bind(&Z::g, this, _1)(x);
>       }
>   };
>
> -- 
> Dave Abrahams
> Boost Consulting
> www.boost-consulting.com
>
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-- Jaakko Järvi                             email: 
jajarvi_at_[hidden]
-- Post Doctoral Fellow                   phone: [phone]
-- Pervasive Technology Labs         fax:   [phone]
-- Indiana University, Bloomington