Am Montag, dem 04.12.2023 um 19:51 +0100 schrieb Jakub Jelinek: > 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).
In C++ you can erase the type with std::function. C is missing a function pointer type which can encapsulate the static chain on all archs (not only for nested functions, also for language interoperability). Martin >
