Re: [boost] Call for interest - BOOST_AUTO_FUNCTION

Subject: Re: [boost] Call for interest - BOOST_AUTO_FUNCTION
From: Matt Calabrese (rivorus_at_[hidden])
Date: 2010-10-17 14:16:51

On Sun, Oct 17, 2010 at 5:32 AM, David Abrahams <dave_at_[hidden]> wrote:

> At Fri, 15 Oct 2010 19:22:16 -0400,
> Matt Calabrese wrote:
> >
> > To see how the macro is used go here: http://codepaste.net/4u34ma
>
> Nice!!  Now are you ready to write BOOST_PARAMETER_AUTO_FUNCTION?  :-)
>

Ha. You know, I actually considered using Boost.Parameter internally for its
type template features before opting for just specializations, but for some
reason I never even thought of trying to support Boost.Paramter
functions. Perhaps for release 10 :p

On Sun, Oct 17, 2010 at 5:32 AM, David Abrahams <dave_at_[hidden]> wrote:

> Questions
>
> * The "keywords" are getting a bit long.  Could you think of shorter
>  names?  Super bonus for finding a way to make them highlight
>  distinctively ;-)

I could certainly change requires_expression to requires_expr or anything
else that makes sense.  I'm not tied to anything in particular

When you say highlight, do you mean try to reuse more C++ keywords so they
highlight in IDEs, something like I do with "return" (and I guess "requires"
if C++ were to eventually get concepts)? I could use "break" instead of
"end". "explicit" might make sense for explicitly specifying the return type
as opposed to "result_type", though I feel like the latter may be more
clear. Maybe I could use "if" instead of "requires". If you have any other
suggestions, let me know. I'm all for something like that as long as the
keywords make sense.

> * is it possible to make all return types lazily computed, so there's
>  no need for lazy_result_type?  I'm not saying I see how to do this,
>  but you might :-)
>

Definitely. I could make it work like mpl::apply (I think that's a feature
of apply unless I'm mistaken) and just use ::type if its there, otherwise
use the type itself. In the code right now I implement result_type with
lazy_result_type anyway by wrapping it in mpl::identity.

> * What is (end) and where is it needed?

Ah, yeah, I should have been more clear on that. Perhaps I'll make a more
descriptive error message if you misuse it. "end" is required when you want
to end a function header such as to either separate the declaration from the
implementation, or to use the macro with a multi-line function. You can only
use it if you have explicitly specified a return type. You can't use it
after a "return", but rather, you use it instead of return. If you declare a
function with "end" you must also define it with "end", otherwise your
declaration will be for a different function than your definition (ouch!).
One reason why you may wish to use "end" even when you're not separating
declaration from implementation is if you are using BOOST_AUTO_FUNCTION only
for "requires" or "requires_expression" rather than automatic return type
deduction, and it's difficult to convert your function template to a
1-liner.

If that was confusing, I assure you I'll try to explain it better in the
docs.

-- 
-Matt Calabrese