Hi,
Richard Guenther <richard.guent...@gmail.com> skribis:
> 2012/3/16 Ludovic Courtès <ludovic.cour...@inria.fr>:
>> Hi,
>>
>> After writing an Autoconf macro that determines whether to build
>> plug-ins with gcc or g++ [0], I realized that nested functions, which my
>> plug-in uses extensively, are not supported in C++.
>>
>> Any suggestions on how to address this?
>
> Don't use nested functions ;) GCC is supposed to be buildable with an ISO C99
> compiler which does not support nested functions either.
Right, but the nice thing with GCC plug-ins is they can be implemented
using all GNU extensions.
Nested functions can serve as the basis for some form of functional
programming, which some of the APIs lend themselves to very well.
For instance, the plug-in at [0] contains things like:
tree task = task_implementation_task (fn);
tree build_parameter (const_tree lst)
{
tree param, type;
type = TREE_VALUE (lst);
param = build_decl (DECL_SOURCE_LOCATION (task), PARM_DECL,
create_tmp_var_name ("parameter"),
type);
DECL_ARG_TYPE (param) = type;
DECL_CONTEXT (param) = task; /* ← closed over variable */
return param;
}
DECL_ARGUMENTS (task) =
map (build_parameter,
list_remove (void_type_p,
TYPE_ARG_TYPES (TREE_TYPE (task))));
What if this snippet were to be written in ANSI C99? The whole ‘map’
paradigm couldn’t be used, because there’d be no way to close over a
local variable.
What about writing it in C++? Function objects could be passed around
to achieve a similar result, at the expense of conciseness and
interoperability with C.
This is an unfortunate collateral damage, IMO.
Thanks,
Ludo’.
[0]
https://gforge.inria.fr/scm/viewvc.php/trunk/gcc-plugin/src/starpu.c?view=markup&root=starpu
