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Subject: Re: Typedef rule

Re: Typedef rule

From: Thomas Martitz <kugel_at_rockbox.org>
Date: Fri, 29 Nov 2013 10:08:42 +0100

Am 29.11.2013 09:27, schrieb Thomas Martitz:
> Hello,
>
> as you know we have a "no typedef rule" in our guidelines. However
> there are a few problems with it when applied to integral types:
>
> * Portability is reduced, for example we use unsigned for thread ids
> but pthread uses unsigned long (I have some work where we can use
> pthreads, at least in parts). This could be handled better with a
> typedef.
> * Readability is reduced, for example we use long for our tick. IMO
> readability/expressiveness would be improved by refering to a "tick_t"
> instead of ordinary long.
> * Type checking is prevented, for example gcc could do better type
> checking with proper typedefs. It's easy to think "I can use int
> instead of long" when the global tick really needs to be a long.
>
> The Linux kernel coding guidelines have summarized the issues even
> better: https://www.kernel.org/doc/Documentation/CodingStyle (chapter 5).
>
> Therefore I propose that we relax the typedef rule and allow typedefs
> for integral types (only) when reasonable. This would basically be
> adopting the Linux kernel guideline w.r.t. to typedefs, except they
> allow typedefs for "totally opaque objects (where the typedef is
> actively used to _hide_ what the object is)."
>
>
> In essence:
> - No typedef for structs and unions. These types help with the
> aforementioned problems by themselves.
> - No typedef for pointers. Hiding a pointer between some type remains
> silly.
> - No typedef for trivial ints, like normal counters (except tick) or
> something like that.
> - Allow typedefs where reasonable, i.e. where it helps enforcing a
> specific type, improves readability and portability.
> - Allow typedefs for void, as to give "void *" a more telling type.
>
> I'd like to trust our developers to weigh up what's reasonable.

I was made aware that we should probably also adopt the above exception
about totally opaque types, for cases where a type is a an integral type
on platform a and some pointer on platform b (as is the case with
pthread_t, apparently).

Therefore I'd like to modify my proposal:

  (1) No typedef for structs and unions. These types help with the
aforementioned problems by themselves. Don't typedef just to avoid
writing out "struct" and "union".
  (2) No typedef for trivial ints, like normal counters (except tick) or
something like that.
  (3) Allow typedefs where reasonable for integral types, i.e. where it
helps enforcing a specific type, improves readability and portability.
  (4) Allow typedefs for void, as to give "void *" a more telling type.
  (5) Generally no typedef for pointers. Hiding a pointer between some
type remains discouraged except in one case: Hiding that the type is a
pointer at all, when the type is strictly used to identify an object
(compatible to long/intptr_t). Typedefing a pointer might be okay if it
points to an incomplete struct/union. This case is actually similar to
(3) where you typedef intptr_t to something better named.

Best regards.
Received on 2013-11-29


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