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Subject: Re: Typedef rule

Re: Typedef rule

From: Felix Lighter <felix.lighter_at_gmail.com>
Date: Fri, 29 Nov 2013 09:53:09 -0500

Agreed on all counts.

On 29 November 2013 09:14, Amaury Pouly <amaury.pouly_at_gmail.com> wrote:
> 2013/11/29 Thomas Martitz <kugel_at_rockbox.org>
>>
>> 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.
>
> Actually I was not aware that we had a typedef rule and I absolutely think
> your proposal is reasonable. I think proper typing when properly used can
> greatly enhance the code quality. So go for it !
Received on 2013-11-29


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