Re: [Boost-users] [parameter] Weird behavior with bools

Subject: Re: [Boost-users] [parameter] Weird behavior with bools
From: Ryan McConnehey (mccorywork_at_[hidden])
Date: 2010-08-29 02:56:07

David Abrahams wrote:
> At Wed, 25 Aug 2010 22:48:57 -0700,
> Ryan McConnehey wrote:
> > I'm new to the parameter library and started with a simple example to 
> > get my feet wet.  The first problem I'm having is with type 
> > restriction.  The "name" variable is being restricted to a boolean 
> > type.  This doesn't seem to be enforced since I can pass this variable a 
> > value of 15 and get this same value out.  Currently my output has "name 
> > = 15" and I expected the output to be "name = 1".  Did I not correctly 
> > enforce the type?
> >   
>
> Looks like a bug to me.  Daniel?
>
> > The second problem is with the default value of my variable.  I thought 
> > if the variable wasn't used then the third parameter, in the 
> > declaration, is used for instantiation of that variable.  I thought that 
> > meant I could do this "m_name(args[_name])".  The compiler gives an 
> > error saying the operator[] can't deduce the arguments.  What did I not 
> > do that would allow this behavior.
> >   
>
> Ditto, looks like a bug.  If we don't already have tests for these
> cases, we should.
>
> > Thank you for your time in helping me out.
> >
> > Ryan
> >
> >
> > BOOST_PARAMETER_NAME(name)
> >
> > struct myclass_impl
> > {
> >     template <class ArgumentPack>
> >     myclass_impl(ArgumentPack const& args)
> >     : m_name(args[_name | false])
> >     //: m_name(args[_name]) //gives a compile error
> >     {
> >       std::cout << "name = " << m_name << std::endl;
> >     }
> >
> > private:
> >   int         m_name;
> > };
> >
> > struct myclass : public myclass_impl
> > {
> >     BOOST_PARAMETER_CONSTRUCTOR(
> >         myclass, (myclass_impl), tag
> >       , (optional
> >           (name, (bool), bool(false)))) // no semicolon
> > };
> >
> > int main(int argc, char* argv[])
> > {
> >   myclass x(_name = 15);
> >
> > return 0;
> > }
> >   

Thanks for the update.  If this is indeed a bug I look forward to
seeing it fixed.

Ryan