Re: [boost] [bind] class template 'value' can corrupt compilability of sound code: Ticket #5141

Subject: Re: [boost] [bind] class template 'value' can corrupt compilability of sound code: Ticket #5141
From: Jeffrey Lee Hellrung, Jr. (jhellrung_at_[hidden])
Date: 2011-01-29 18:16:10

On 1/29/2011 3:04 PM, Joachim Faulhaber wrote:
> Hi Peter, list,
[...]
> This is a minimal program to demonstrate how 'class value' can confuse msvc:
> //=========================================================
> #include<boost/config.hpp>
> //--- from boost/bind/bind.hpp(112)
> namespace _bi{
>      template<class T>  class value{};
> }
>
> //--- affected code ---------------------------------------
> template<class Type>  struct some_attribute
> {
>      BOOST_STATIC_CONSTANT(int, value = 0);
> };
>
> template<class Type>  struct some_predicate
> {
>      BOOST_STATIC_CONSTANT(bool,
>          value = ( some_attribute<Type>::value<  0)
>                  //error C2059: syntax error : ')'
>                  //IF class template value defined before

Does adding parentheses, i.e.,
            value = ( (some_attribute<Type>::value) < 0 )
help?  If so, it could be an alternative to renaming the "value" 
template...although it could require quite a few more changes to boost 
code...

>          );
> };
> //=========================================================
>
> Although I frankly don't know, how exactly msvc is derailed, it seems
> to have problems with 'value' in
>
> some_attribute<Type>::value<  0

...worth filing a bug in the MS Connect database?

> a construction that is extremely frequent due to meta programming
> conventions introduced by Dave's and Aleksey's boost::mpl. So for a
> fix I tried to rename 'class value' by something else like 'class
> _value'. Fortunately this is possible, because the class template is a
> local implementation object used in boost/bind/bind.hpp only.

Not sure how many value struct templates there are under boost, but I 
wouldn't be surprised if there were another one for which renaming were 
*not* an option...

> After renaming, I successfully ran all tests from boost/bind. Find the
> patch file attached. I have also filed a ticket
> https://svn.boost.org/trac/boost/ticket/5141

- Jeff