On 2/21/23 19:38, Eric Blake wrote:
> On Tue, Feb 21, 2023 at 01:24:17PM +0000, Richard W.M. Jones wrote:
>>>>> +++ b/generator/states-connect-socket-activation.c
>>>>> @@ -51,7 +51,7 @@ prepare_socket_activation_environment (string_vector
>>>>> *env)
>>>>> char *p;
>>>>> size_t i;
>>>>>
>>>>> - assert (env->len == 0);
>>>>> + *env = (string_vector)empty_vector;
>>>>
>>>> Do you actually need to cast this?
>>>
>>> This is not a cast, but a C99 compound literal. And yes, it is
>>> necessary, as empty_vector is just:
>>>
>>> #define empty_vector { .ptr = NULL, .len = 0, .cap = 0 }
>>>
>>> So this is *not* initialization, but assignment. We have a string_vector
>>> object (a structure) on the LHS, so we ned a structure on the RHS as
>>> well. The compound literal provides that (unnamed, automatic storage
>>> duration) structure. It looks like a cast (quite intentionally, I'd
>>> hazard), but it's not a cast.
>>
>> OK it's not a cast, but struct assignment is well defined so is the
>> change necessary?
>
> Struct assignment requires a source struct. Either a named one (which
> we do not have here without declaring one), or via a compound literal
> (which resembles a cast).
>
> It sounds like it would be nice to have a type-specific macro, as in
> 'empty_string_vector', 'empty_int_vector', and so on, per each use of
> DEFINE_VECTOR_TYPE() - but while our one macro can easily declare
> other type-specific functions, you can't really use the preprocessor
> to define further type-specific macros. So having to tell the user to
> supply their own type name when reusing the type-agnostic initializer
> portion of a compound literal is not too bad in the long run, although
> it might be worth documenting the practice in vector.h.
>
... another follow-up item :)
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