ImportC and #pragma pack

[Walter Bright]

On 9/28/2021 5:46 PM, Guillaume Piolat wrote:
> On Tuesday, 28 September 2021 at 23:16:28 UTC, Walter Bright wrote:
>>
>> Anyhow, pointing out non-standard constructs that can be replaced with 
>> standard ones
> 
> 
> But _Alignas strictly can't replace #pragma pack.
> 
> D's align(), C's _Alignas, and #pragma pack have 3 different semantics.
> 
> See https://ideone.com/bv6mET
> 
> - #pragma pack can only _reduce_ alignment requirements within a struct, NOT 
> introduce additional padding
> 
> - _Alignas, contrarily, can only be used to _increase_ alignment and introduce 
> padding, but cannot reduce the natural alignment of a field.
> 
> - D's align can both reduce and increase field alignment, which is of course the 
> better option (https://ideone.com/TLSZUO)
> 
> 

C11 6.7.5-4 sez: "The combined effect of all alignment attributes in a 
declaration shall not specify an alignment that is less strict than the 
alignment that would otherwise be required for the type of the object or member 
being declared."

Which I interpret to mean it can be allowed as an extension.