[Boost-users] Re: Why using boost::function with lambda requires RTTI?

From: David Abrahams (dave_at_[hidden])
Date: 2005-01-07 08:27:29

Douglas Gregor wrote:
> On Jan 6, 2005, at 5:25 PM, Philippe Mori wrote:
>> When I compile the code I get the following warning "RTTI option is
>> disabled" at the line with the following macro call
>> BOOST_FUNCTION_COMPARE_TYPE_ID in function
>> boost::detail::function::functor_manager::manage().
> 
> Function allows you to ask about the return type (via 
> boost::function<...>::type()) and to extract the type, for which it 
> needs RTTI. However, this feature could be #ifdef'd out. We had 
> (briefly) discussed adding a BOOST_NO_RTTI macro for this purpose back 
> in September. Perhaps it's time to reopen that discussion.
> 
>> Also, a lambda function like (((1.0 * _1 + 2.0) * _1 + 3.0) * _1 + 
>> 4.0) * _1
>> + 5.0 cause my data segment to increase of 6K which is huge when the 
>> limit
>> is 64K...
>>
>> Using a static function (and not using boost::lambda) instead does not 
>> cause
>> such increase of the use of the data segment.
> 
> I'm surprised that the increase is so large, but not that it exists. 
> _1, _2, etc. are namespace-level variables (by necessity) and will be 
> replicated in each translation unit where they are used.

But they shouldn't be.  We have to get them out of the unnamed namespace
anyway for ODR reasons.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com