Re: [PATCH v6 04/14] block/amend: separate amend and create options for qemu-img

[Eric Blake <eblake@redhat.com>]

On 5/15/20 1:22 AM, Max Reitz wrote:

>>>
>>>> +        QCOW_COMMON_OPTIONS,
>>>> +        { /* end of list */ }
>>
>> ...the intended usage is to use the macro name followed by a comma, so
>> including a trailing comma in the macro itself would lead to a syntax
>> error.
> 
> But why is that the indended usage?  Is there something in our coding
> style that forbids macros that don’t allow a separator to be placed
> after them?

If we have more than one such macro, it is easier to write and indent 
(especially when using your editor's ability to decipher enough syntax 
to suggest how to indent):

myarray = {
   COMMON_ELEMENTS,
   MORE_ELEMENTS,
   { /* end of list */ }
};

than it is:

myarray = {
   COMMON_ELEMENTS
   MORE_ELEMENTS
   { /* end of list */ }
};

which in turn implies that it is better to NOT stick a trailing comma in 
the macro itself.  Similarly, for macros intended to replace statements, 
we tend to avoid the trailing ; in the macro itself, because it is 
easier to read:

{
   code;
   MACRO();
   more code;
}

than it is:

{
   code;
   MACRO()
   more code;
}

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org