Re: [boost] yomm2 - open methods

Subject: Re: [boost] yomm2 - open methods
From: Jean-Louis Leroy (jl_at_[hidden])
Date: 2018-01-21 20:22:21

Thanks for the comments.

I am still hesitating about some of the names and APIs. The library is
pre-version 1.0.0, and it's the time to get things right.

I am still hesitating about the syntax for defining a method
(overridern). I could easily support:

// no return type here
// ---------V
YOMM2_BEGIN(kick, (Dog& dog)) {
  return "bark";
} YOMM2_END;

It breaks the symmetry with YOMM2_DECLARE though.

Now onto your points...

> - I feel like it should be possible to get rid of YOMM2_END
>   by moving the function body out-of-line or using a lambda
>   or something.

Of course I would like to get rid of YOMM2_END, but I haven't yet found a way
of doing that that also ensures that the body of the method can be inlined
inside the wrapper that casts the virtual arguments. I trie with lambdas to
back in 2014. Then maybe I've overlooked something, if you have an idea...

> - The documentation isn't clear on how the one-definition-rule
>   applies (unless I missed it).  My default assumption would
>   be that YOMM2_DEFINE for a given overload should appear in
>   exactly one translation unit, and that YOMM2_DECLARE and
>   YOMM2_CLASS may appear in multiple translation units so
>   long as the declarations are identical, but I notice that
>   they're /all/ using unnamed namespaces.  All of your examples
>   only use a single source file, so I can't really guess your
>   intentions from usage either.

Indeed I should be more explicit about this. As you guessed, YOMM2_DECLARE
should go is header file worthy - it just defines an inline function and
delcares a hidden function that is just used to guide the overload resolution.

YOMM2_DEFINE is for *defintions* and as such only one is allowed per process;
they're for .cpp files.

YOMM2_CLASS is borderline. Normally it should be called once, whereever that
happens - but it tolerates being called any number of times. That's for coping
with situations where the same class may have several associated type_info
objects - what I have in mind here is dynamically loaded Windows DLLs.

I will improve the documentation...

> - I'm curious why I would ever want to use the "cute" names
>   when they're actually longer than the YOMM2 names.

I would use them ;-) They're more readable, and no uppercase loud. YOMM2 is an
obscure acronym (Yorel's Open Multi Methods) that I picked to avoid name
clashes. Lowercase names look more like keyworks.

But indeed maybe I should write the entire doc and examples in terms of YOMM2*
macros and de-emphasize the "cute" macros.

J-L