Re: [boost] [contract] syntax redesign

Subject: Re: [boost] [contract] syntax redesign
From: lcaminiti (lorcaminiti_at_[hidden])
Date: 2011-05-31 17:59:08

Matt Calabrese wrote:
> 
> On Tue, May 31, 2011 at 5:21 PM, lcaminiti <lorcaminiti_at_[hidden]>
> wrote:
>>
>> If the return type is a "keyword" known a priori like void then no
>> parenthesis should be needed.
> 
> 
> Oh, so you just special-cased some keywords and the rest require
> parentheses? That's good. The only criticism I have of that is that it's
> inconsistent. I had some special-casing to eliminate parentheses, similar
> to
> what you are doing, but I ultimately sided on being consistent over
> everything else. That's obviously just my opinion, so I'm not saying you
> should definitely change it, it's just something to consider.
> 

Yes, I was also concerned about inconsistency so I decided that the syntax
will always accept parenthesized types. You can (but don't have to) omit the
parenthesis for a known "keyword". This way users can choose as they wish.

In other words, the following will both be accepted by the same macros:

    CONTRACT_FUNCTION( (void) (f)() ) // (1)

    CONTRACT_FUNCTION( void (f)() ) // (2)

If you are worry about consistency, you use (1). If you are worried abut
extra parenthesis, you use (2).

> Also, given your description (using IS_UNARY), it sounds as though your
> current implementation cannot handle return types that have top-level
> commas. For instance, you can't return a boost::array< int, 2 > directly
> without using a typedef (and if that return type is dependent on the
> function's template parameters then you could potentially be stuck). I
> highly recommend that you use variadic macros here to directly check if
> it's
> anything parenthesized other than empty. It looks like you're already
> 

Boost.Local's BOOST_IDENTITY_TYPE can be used to handle un-parenthesized
commas within macro parameters (see
http://svn.boost.org/svn/boost/sandbox/local/boost/utility/identity.hpp).

> relying on variadic macros for your parameter lists, so you wouldn't be
> introducing further compiler requirements.
> 

Similarly to Boost.Local, the syntax will require parenthesis on
preprocessors without variadics:

    CONTRACT_FUNCTION( void (f)( (int x) (int y) ) ... ) // no variadics
must use this

With variadics, you can still use the above or alternatively the same macros
will accept commas:

    CONTRACT_FUNCTION( void (f)( int x, int y ) ... ) // variadics can (but
don't have to) use this

>> I have done some experimentation that indicates this syntax _should_ be
>> possible but it's not actually implemented yet so... we'll see :)
> 
> It's definitely possible, yes.
> 

--Lorenzo

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