Re: [Boost-users] [Parameter] Constructors and more

From: David Abrahams (dave_at_[hidden])
Date: 2006-03-01 21:45:02

"Johan Nilsson" <r.johan.nilsson_at_[hidden]> writes:

> I've experimented some with defining a parameter::parameters specification 
> and use (the undocumented) BOOST_PARAMETER_MEMFUN, but that obviously 
> doesn't work (forwarding, return values and constructors don't
> mix). 

Generally you have to forward the overloaded constructors to a base
class constructor that takes the ArgumentPack and does all the "real"
work.  IOW, you may need to insert a base class in the hierarchy just
for the purpose of construction.

> It 
> should be possible (I think) to define a BOOST_PARAMETER_CTOR macro that 
> generate the ctor overloads and forwards to a setter method instead of the 
> other way around.

It won't  be general enough to initialize constant or reference
members.

> 2. Is there a way of detecting whether an argument was passed using position 
> or name? 

Nope.

> Or, even better, is there a way of restricting the arguments to 
> only be passed by name using the parameters specification?

Nope.  Why do you want to do that?

> 3. Not a question really, but having a default arity of 5 seems awfully low 
> to me. I hit that limit on first usage, and as the named parameters are 
> supposed to be used in the interface of my wrapping library, forcing users 
> to define BOOST_PARAMETER_MAX_ARITY "globally" feels a bit like asking for 
> someone coming up and asking me to decode some compile errors.

Reasonable point.  Daniel, what do you think?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com