Re: [Boost-users] lambda boost::array operator[] error

From: Jaakko Järvi (jarvi_at_[hidden])
Date: 2006-09-30 19:57:36

The return type deduction mechanism of boost lambda does not
recognize boost::array, and does not know what the return type
of the subscription mechanism is:

Try:

ret<int&>(_1[0]) = 10, ret<int&>(_1[1]=9 )

(I didn't, but hopefully you get the idea).

   Jaakko

On Sep 30, 2006, at 6:13 PM, Levent Yilmaz wrote:

> Hi All,
>
>
> Please take a look these two similar set of statements. One uses  
> vector,
> the other boost::array :
>
> /**/
>
> using std::vector;
> using boost::array;
> using std::for_each;
> using boost::lambda::_1;
>
> // This one compiles:
> typedef vector<int> Vector;
> Vector v(2);
> vector<Vector> vv(5,v);
> for_each( vv.begin(), vv.end(), (_1[0]=10, _1[1]=9) );
>
> // This one doesn't:
> typedef array<int,2> Array;
> vector<Array> va(5);
> for_each( va.begin(), va.end(), (_1[0]=10, _1[1]=9) );
>
> /**/
>
> With MSVC 7.1, I get:
> =====
> d:\boost\include\boost-1_33_1\boost\lambda\detail 
> \operator_lambda_func_base.hpp(237):
>   error C2679: binary '=' : no operator found which takes a right-hand
> operand of type 'const  
> boost::tuples::cons<HT,TT>::stored_head_type' (or
> there is no acceptable conversion)
>          with
>          [
>              HT=const boost::lambda::detail::parameter_traits_<const
> int,const boost::lambda::detail::IF<false,const int &,const
> int>::RET>::type,
>
> TT=boost::tuples::detail::map_tuple_to_cons<boost::tuples::null_type,b 
> oost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_t 
> ype,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::n 
> ull_type,boost::tuples::null_type,boost::tuples::null_type,boost::tupl 
> es::null_type>::type
>          ]
> ======================================================
>
>
> With gcc 3.4.4, I get a moderately sized novel, whose last line reads:
> =====
> /usr/local/include/boost/lambda/detail/ 
> operator_lambda_func_base.hpp:136:
> error: conversion from `int' to non-scalar type
> `boost::lambda::detail::unspecified' requested
> =======================================================
>
> This is boost version 1.33.1.
> What could be wrong?
>
> thx
>
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