[Python-Dev] Can we use "designated initializer" widely in core modules?

[Brett Cannon]

On Mon, 16 Jan 2017 at 22:34 INADA Naoki <songofacandy at gmail.com> wrote:

> Hi.
>
> ---
> This discussion is started in http://bugs.python.org/issue29259, and
> there is separated issue at http://bugs.python.org/issue29260 .
> But I want to see more comments, before issue 29259 is committed.
> ---
>
> Since Python 3.6, some of C99 features are accepted in PEP 7.
> "designated initializer" is one of them.
>
> PEP7 says  "designated initializers (especially nice for type
> declarations)"
>
> For example, issue 29259 is adding new slot named tp_fastcall in type
> structure.
> Without designated initializer, there are many diffs like this:
>
>      0,                                  /* tp_free */
> +    0,                                  /* tp_is_gc */
> +    0,                                  /* tp_bases */
> +    0,                                  /* tp_mro */
> +    0,                                  /* tp_cache */
> +    0,                                  /* tp_subclasses */
> +    0,                                  /* tp_weaklist */
> +    0,                                  /* tp_del */
> +    0,                                  /* tp_version_tag */
> +    0,                                  /* tp_finalize */
> +    (fastternaryfunc)attrgetter_call,   /* tp_fastcall */
>  };
>
> With designated initializer, it becomes:
>
>      0,                                  /* tp_free */
> +    .tp_fastcall = (fastternaryfunc)attrgetter_call,
>  };
>
> It's readable, and easy to review.
> Without designated initializer, it's difficult to find copy & paste
> mistake.
> (Can you find if I missed /* tp_is_gc */ line in first patch?)
>
> On the other hand, this syntax is C99 specific.
> C++ doesn't accept this syntax, even for newest C++14.
> Using this feature make it's difficult to use (subset of) C++ features
> in the future.
>

At this point I really doubt we will ever switch to C++ so I don't think
making any such theoretical transition is worth holding back cleaner code.
Plus if this isn't going into a header file that some C++ extension module
is going to be pulling in then third-party C++ code should be shielded from
the incompatibility.


>
>
> So, how widely can we use "designated initializer"?
> Only in Modules (_asyncio uses it already)?
> Or almost everywhere (Objects/ and Python/)?
>

I say everywhere we can (and that also means we should probably update the
xx* files in Modules/).

-Brett


>
> I want to get decision before issue 29259 is committed, because it
> will add many "0, /* tp_xxx */"
>
> Regards,
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