Re: [boost] [parameter] Tutorial checked in

From: Rob Stewart (stewart_at_[hidden])
Date: 2005-07-22 12:17:25

From: David Abrahams <dave_at_[hidden]>
> Rob Stewart <stewart_at_[hidden]> writes:
> > From: David Abrahams <dave_at_[hidden]>
>
>> I didn't look, but it sounded odd that one could pass an int,>
>char *, std::complex, etc.
> 
> Well, you can at least pass anything to the keyword's
> operator=.Whether or not the depth_first_search function
> compiles is anothermatter.

OK.

> Pedantry aside, what else is there?

I suppose there are two levels of pedantry in this case.  One is
in the tutorial itself, and the other was due to my talking about
passing references.

> How's this?
>   A keyword object has a pair of ``operator=`` overloads that
> ensure  we can pass anything—temporary or not,
> ``const`` or not—by name,  while preserving the
> mutability of non-temporaries:
>   .. parsed-literal::
>     template <class A>                  // handles non-const,     |ArgumentPack| operator=(A&);       // non-temporary objects
>     template <class A>                  // handles const objects    |ArgumentPack| operator=(A const&); // and temporaries
>   However, when an “out” parameter is passed
> positionally, there's no  keyword object involved.  With our
> ``depth_first_search`` overload  set above, the ``color_map``
> will be passed by ``const`` reference,  and compilation will
> fail when mutating operations are used on it.  The simple
> solution is to add another overload that takes a  non-``const``
> reference in the position of the “out”
> parameter:

That should do it!

-- 
Rob Stewart                           stewart_at_[hidden]
Software Engineer                     http://www.sig.com
Susquehanna International Group, LLP  using std::disclaimer;