RE: [boost] BOOST_STATIC_CONSTANT problem

From: Aleksey Gurtovoy (alexy_at_[hidden])
Date: 2001-06-27 08:59:12

Steve Cleary wrote:
> Last night I converted some code over to use the BOOST_STATIC_CONSTANT
> macro, and ran into a problem: any ICE whose value is determined by a
> template class that takes two or more parameters (*including* the
> metaprogramming helpers provided by <boost/type_traits/ice.hpp>) cannot be
> declared with this macro.
> 
> That's a mouthful, so here's an example from "ice_guidelines.htm":
>   ::boost::type_traits::ice_or<ICE1,ICE2>::value
> but you can't declare it using BOOST_STATIC_CONSTANT:
>   BOOST_STATIC_CONSTANT(bool, val =
> ::boost::type_traits::ice_or<ICE1,ICE2>::value);
>                                                         syntax error ^
> 
> The problem is that there isn't a way to use an expression 
> containing commas as a value for the 'assignment' macro 
> argument (wrapping it in parenthesis, the standard way to pass 
> commas in macro arguments, will result in a syntax error in this case).

What you need to do is to wrap in parenthesis
"::boost::::type_traits::ice_or<>::value" expression, e.g.

BOOST_STATIC_CONSTANT(bool, val =
(::boost::type_traits::ice_or<ICE1,ICE2>::value));

It's not the fisrt time the question arises, so probably we need to put this
in the paper.

Aleksey