On Mon, Dec 04, 2023 at 01:27:32PM -0500, Siddhesh Poyarekar wrote:
> [Branching this into a separate conversation to avoid derailing the patch,
> which isn't directly related]
>
> On 2023-12-04 12:21, Martin Uecker wrote:
> > I do not really agree with that. Nested functions can substantially
> > improve code quality and in C can avoid type unsafe use of
> > void* pointers in callbacks. The code is often much better with
> > nested functions than without. Nested functions and lambdas
> > (i.e. anonymous nested functions) are used in many languages
> > because they make code better and GNU's nested function are no
> > exception.
> >
> > So I disagree with the idea that discouraging nested functions leads
> > to better code - I think the exact opposite is true.
>
> I would argue that GNU's nested functions *are* an exception because they're
> like feathers stuck on a pig to try and make it fly; I think a significant
> specification effort is required to actually make it a cleanly usable
> feature.
Why? The syntax doesn't seem to be something unexpected, and as C doesn't
have lambdas, one can use the nested functions instead.
The only problem is if you need to pass function pointers somewhere else
(and target doesn't have function descriptors or something similar), if it
is only done to make code more readable compared to say use of macros, I
think the nested functions are better, one doesn't have to worry about
multiple evaluations of argument side-effects etc. And if everything is
inlined and SRA optimized, there is no extra cost.
The problem of passing it as a function pointer to other functions is
common with C++, only lambdas which don't capture anything actually can be
convertible to function pointer, for anything else you need a template and
instantiate it for a particular lambda (which is something you can't do in
C).
Jakub
