Re: [boost] [parameter] Tutorial checked in

From: Rob Stewart (stewart_at_[hidden])
Date: 2005-07-22 10:02:45

From: David Abrahams <dave_at_[hidden]>
> Rob Stewart <stewart_at_[hidden]> writes:
> > From: David Abrahams <dave_at_[hidden]>
> >
> >    On the other hand\x{2014}as you may recall from the parameter
> >    table\x{2014}``color_map`` is an \x{201C}out\x{201D}
> >    parameter, so it really should be passed by non-const
> >    reference.
> >
> > Note that "color_map" and "out" are quoted significantly
> > differently with no apparent reason.
> 
> No, ``color_map`` isn't quotation; it's markup for "code font."  Look
> at the HTML.

I was looking at it in the browser.  I saw "``color_map``" and
"<fancy open quote>out<fancy close quote>" so I saw no "code
font" markup.  Unless I'm misunderstanding you, something is
wrong.

> >    A keyword object has a pair of operator= overloads that ensure
> >    we can pass anything by name, but when an \x{201C}out\x{201D}
> >    parameter is passed positionally, that's no help: in this
> >    case, core::depth_first_search would end up with a const
> >    reference to the color_map and compilation will fail when
> >    mutating operations are used on it.
> >
> > That's a long sentence and did you really mean to say "we can
> > pass *anything*" (emphasis mine)?
> 
> Yep.

I didn't look, but it sounded odd that one could pass an int,
char *, std::complex, etc.

> > Perhaps this would be better:
> >
> >    A keyword object has a pair of operator = overloads that
> >    ensure we can pass references to const or non-const objects by
> >    name, 
> 
> You don't get to pass references to anything in C++.  You pass the
> object referred to by a name or expression and the callee decides
> whether it goes by reference.

Yeah, I misspoke (miswrote?).  I was referring to the parameter
type when I should have been discussing the allowable argument
types.

> Also, the point is that you can pass both lvalues and rvalues, or
> temporaries and non-temporaries, not that the objects can be const or
> non-const.  You can do that just fine with a single templated function
> taking a T& (T will be deduced as U const when the object is constant).

Pedantry aside, that's not the same as *anything*.

> >    but when an "out" parameter is passed positionally,
> >    that's no help.  In that case, core:;depth_first_search would
> >    end up with a...."

What about splitting the sentence into two?

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