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

Subject: Re: [Boost-users] [parameter] Weird behavior with bools
From: David Abrahams (dave_at_[hidden])
Date: 2010-08-28 01:49:24

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;
> }

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com