Re: [boost] [proto] _value doesn't enforce zero arity

Subject: Re: [boost] [proto] _value doesn't enforce zero arity
From: Eric Niebler (eric_at_[hidden])
Date: 2009-04-06 23:49:33

troy d. straszheim wrote:
> I see some funny behavior when misusing _value:
> 
> #include <boost/proto/proto.hpp>
> 
> namespace bp = boost::proto;
> 
> int main(int, char**)
> {
>   bp::terminal<int>::type t = {0};
> 
>   bp::terminal<int>::type hmm = bp::value(t * 2);
>   bp::terminal<int>::type uhm = bp::_value()(t * 2);
> 
>   bp::terminal<const int&>::type hrm = bp::value(2 * t);
>   bp::terminal<const int&>::type feh = bp::_value()(2 * t);
> }
> 
> Which does compile..  but the docs say that _value requires an 
> expression of zero arity.
<snip>

Yep, it compiles, and yep, it violates the preconditions. I choose not 
to enforce the preconditions because doing so would cause extra template 
instantiations and lengthen compile times. As long as valid programs 
compile and do the right thing, I'm happy.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com