Re: [boost] [vmd] Library Review

Subject: Re: [boost] [vmd] Library Review
From: Edward Diener (eldiener_at_[hidden])
Date: 2014-09-13 17:59:33

On 9/13/2014 9:44 AM, Paul Mensonides wrote:
> (apologies for the late review)
>
> -- Design --
>
> Many of the utility components of the library have decent design.  There
> are, however, a couple of aspects of the design that I dislike, and they
> touch on a large chunk of the library.  These concerns all revolve
> around the registration, recognition, parsing, and limitations of
> various "v-types" and "v-sequences".
>
> I do not yet see a strong use case for the "v-key"/"v-identifier"
> recognition scenario, as opposed to just registering a "v-identifier".
> For example,
>
>      #define BOOST_VMD_MAP_<v-key><v-identifier>
>      // ...
>
>      BOOST_VMD_IS_IDENTIFIER(<v-seq>, <tuple-of-v-keys>)
>
> Perhaps Edward can enlighten me about the use-cases for which this is
> ideal.  I do see some use-cases, but in most cases it requires dispatch
> based on what the particular "v-identifier" it is anyway.
>
> One could do better for this low-level part with registrations such as
> (without a BOOST_VMD_ prefix for brevity)
>
>      #define IDENTIFIER_CIRCLE (CIRCLE),
>      #define IDENTIFIER_SQUARE (SQUARE),
>      #define IDENTIFIER_TRIANGLE (TRIANGLE),
>      #define IDENTIFIER_RECTANGLE (RECTANGLE),
>
> These definitions don't allow one to directly test for specific
> "v-identifiers", but they do allow one to extract registered
> "v-identifiers" from a "v-sequence".
>
> If all such registrations are required to be the same, there is no need
> for separate per-library prefixes.  Macros can be defined multiple times
> if they are defined the same way.
>
> Similarly, the "v-numbers" could be pre-registered by the library as
>
>      #define NUMBER_0 (0),
>      #define NUMBER_1 (1),
>      #define NUMBER_2 (2),
>      // ...

I realized why the registrations have a trailing comma. Brilliant. Thanks !