On 09/01/2012 12:33 AM, Björn Persson wrote:
As maintainer of fedora-gnat-project-common I sometimes work on RPM
use in Ada packages. Every time I define a new macro I have trouble deciding
whether its name should begin with an underscore or not. I know that there is
some technical difference but I've never quite understood what practical
difference it makes.
I've been trying to imitate macros with a similar function, so I defined
_GNAT_project_dir with a leading underscore in analogy with _libdir and
others. Macros containing command line flags for build tools I've defined
without a leading underscore in analogy with optflags, but then there are
_smp_mflags and the hardening macros which have the underscore, and
__global_cflags and __global_ldflags even have two leading underscores.
Could someone explain what difference a leading underscore makes and give some
guidance on when I should use it?
Is a double leading underscore functionally different from a single one, or is
that just some kind of naming convention?
A name is just a name, there's no functional difference. Once upon a
time in a faraway galaxy there might have been, but that's nothing you
need to worry about. These days its just a naming convention, albeit a
rather blurry one.
The bottom line: as long as your macros are "namespaced" (such as your
GNAT/_GNAT prefix) to limit the possibility of clashes with others,
you're technically free to call them whatever you want. Following
existing conventions is not a bad idea though.
- Panu -