Re: [boost] Constructor with parameters -- Lambda

From: albert meyburgh (ameyburgh_at_[hidden])
Date: 2008-06-17 15:31:26

I believe this is a bug in the boost lambda constructor

I have worked around the problem with this wrapper:

template< typename T >
    struct LambdaConstructorWrapper : public boost::lambda::constructor< T >
    {
        typedef T result_type;
    };

and using it as such:

LambdaConstructorWrapper<MyType> myTypeConstructionWrapper;

                std::transform(
                    mycontainer.begin(),
                    mycontainer.end(),
                    std::back_inserter( redcontainer ),
                    boost::bind(myTypeConstructionWrapper, _1,
WHATEVER_PARM));

It seems to behave as expected by adding this one typedef so it's probably a
bug?  unless by design it's not supposed to be used this way for some reason
that I don't see?

On Mon, Jun 16, 2008 at 9:55 AM, albert meyburgh <ameyburgh_at_[hidden]>
wrote:

> Thanks for the input on trying to use boost::lambda::bind instead of
> boost::bind, unfortunately there is no bind in the lambda namespace.
>
> I'm using Boost 1.35, and in my version "namespace lambda" only exists in
> boost\lambda\construct.hpp and only contains a single templated struct
> constructor, there is no bind available :(
>
> Any ideas?
>
> I'm trying all sort of funny syntax variations to no avail...
>
> Message: 4
> Date: Fri, 13 Jun 2008 15:37:58 -0700
> From: "albert meyburgh" <ameyburgh_at_[hidden]>
> Subject: [boost] Constructor with parameters -- Lambda
> To: boost_at_[hidden]
> Message-ID:
>        <35f053b10806131537o4b85769fg84a88bc0c70dddc4_at_[hidden]>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi,
>
> I'm trying to use the lambda constructor provided in boost and it's not
> compiling.
>
> class someclass
> {
> someclass(sometype, int x)
> }
>
> std::vector v<sometype>
> std::vector v2<someclass>
> std::transform( v.begin(),
>                    v.end(),
>                    std::back_inserter( v2 ),
>                    boost::bind( boost::lambda::constructor<someclass>(),
> _1, 5) ); // where 5 is a constant int parameter for x to the constructor
>
> Resulting in
>
> Error    1    error C2039: 'result_type' : is not a member of
> 'boost::lambda::constructor<T>'   boost_1_35_0\boost\bind.hpp    67
> Error    2    error C2146: syntax error : missing ';' before identifier
> 'type'    boost_1_35_0\boost\bind.hpp    67
> Error    3    error C4430: missing type specifier - int assumed. Note: C++
> does not support default-int    boost_1_35_0\boost\bind.hpp    67
> Error    4    error C2208: 'boost::_bi::type' : no members defined using
> this type   boost_1_35_0\boost\bind.hpp    67
> Error    5    fatal error C1903: unable to recover from previous error(s);
> stopping compilation    boost_1_35_0\boost\bind.hpp    67
>
> What is wrong with my syntax?
>
>
> ------------------------------
>
> Message: 5
> Date: Fri, 13 Jun 2008 15:57:59 -0700
> From: Steven Watanabe <watanabesj_at_[hidden]>
> Subject: Re: [boost] Constructor with parameters -- Lambda
> To: boost_at_[hidden]
> Message-ID: <4852FB77.4000902_at_[hidden]>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> AMDG
>
> albert meyburgh wrote:
> >                     boost::bind( boost::lambda::constructor<someclass>(),
> > _1, 5) ); // where 5 is a constant int parameter for x to the constructor
> >
>
> Use boost::lambda::bind.
>
> In Christ,
> Steven Watanabe
>
>
>
> ------------------------------
>
> Message: 6
> Date: Fri, 13 Jun 2008 15:59:14 -0700
> From: Eric Niebler <eric_at_[hidden]>
> Subject: Re: [boost] Constructor with parameters -- Lambda
> To: boost_at_[hidden]
> Message-ID: <4852FBC2.8040606_at_[hidden]>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> albert meyburgh wrote:
> > Hi,
> >
> > I'm trying to use the lambda constructor provided in boost and it's not
> > compiling.
> >
> > class someclass
> > {
> > someclass(sometype, int x)
> > }
> >
> > std::vector v<sometype>
> > std::vector v2<someclass>
> > std::transform( v.begin(),
> >                     v.end(),
> >                     std::back_inserter( v2 ),
> >                     boost::bind( boost::lambda::constructor<someclass>(),
>
> Try boost::lambda::bind() instead of boost::bind().
>
>
> --
> Eric Niebler
> BoostPro Computing
> http://www.boostpro.com
>