Re: [Boost-users] [phoenix] adding const to member_variable bind

Subject: Re: [Boost-users] [phoenix] adding const to member_variable bind
From: Joel de Guzman (joel_at_[hidden])
Date: 2008-11-12 02:23:36

Steven Watanabe wrote:
> AMDG
> 
> Joel de Guzman wrote:
>>> There is no way for result to distinguish between these cases,
>>> even though they are different.
>>
>> Out of curiosity, how does Boost.Bind and Lambda.Bind behave in this
>> regard?
> 
> It looks like:
> a) bind always constifies the return type of a pointer to a data member.
> b) lambda does not strip references in its return type deduction.
> 
[...]
> 
> void boost_phoenix() {
>    namespace phoenix = boost::phoenix;
>    x x_ = {0};
>    phoenix::bind(&x::m, phoenix::val(x_))(); // does not compile
>    phoenix::bind(&x::m, phoenix::ref(x_))() = 1;
>    phoenix::bind(&x::m, phoenix::cref(x_))(); // does not compile
> }

The third is ok with your patch. Anyway, ok, this is a bug due to,
as you noticed, stripping of the top level reference. Seems it's
a limitation of the old result-type scheme. I think it can only
be fixed when we move to the result_of protocol which respects
the references.

Anyway, I added your test (which fails the val(x) test and your
patch (which allows the cref(x) test). I'll keep the failing
val(x) test to remind me to fix this bug.

Regards,
-- 
Joel de Guzman
http://www.boostpro.com
http://spirit.sf.net