Is there a technical reason for not allowing nested function definitions?

Asked Oct 22 '19 at 19:15

Active Oct 22 '19 at 19:27

Viewed 120 times

Why C++ does not allow something like:

int foo(int x) {
    void bar(int x) { return x*x;}
    return bar(x);
}

Disclaimer: I am not asking for the rationale for disallowing it. We can define classes inside functions, in particular functors, and since C++11 lambdas, so actually I do not see the need for it.

However, I wonder if there is some technical limitation/problem that would prevent to allow it. Would it create ambiguities syntax-wise? Other problems that I dont see? Or is the answer perhaps simply: It is not allowed because there is no need for it?

asked Oct 22 '19 at 19:15

463035818_is_not_an_ai

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That syntax comes from K&R C, do you want to ask them? – Slava Oct 22 '19 at 19:17
it is possible with gcc gnuC – OznOg Oct 22 '19 at 19:18
@OznOg oh that actually answers my question ;) – 463035818_is_not_an_ai Oct 22 '19 at 19:18
@OznOg as I understand, not in standard c, but gnu c. Anyhow, there is no technical limitation – 463035818_is_not_an_ai Oct 22 '19 at 19:22
@Mär the duplicate kind of prooves that there is no technical limitation. The q you propose as dupe is more about defining something "function-like" or callable, while I specifically ask for functions. Anyhow I'll add it to the list – 463035818_is_not_an_ai Oct 22 '19 at 19:24
@formerlyknownas_463035818 Thanks for elaboration. – Koenigsberg Oct 22 '19 at 19:24
@Mär no idea waht is going on here. I wanted to add your link to the list of duplciates, but somehow the question has been reopened meanwhile and now I cannot flag as dupe again... – 463035818_is_not_an_ai Oct 22 '19 at 19:26
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@formerlyknownas_463035818 Let me close it and you can add it. – NathanOliver Oct 22 '19 at 19:26
@NathanOliver do you know if I can find out who reopenend the question? Not that it really matters, just curious. – 463035818_is_not_an_ai Oct 22 '19 at 19:28
@formerlyknownas_463035818 You can see that in the timeline: https://stackoverflow.com/posts/58510922/timeline – NathanOliver Oct 22 '19 at 19:29
@NathanOliver thanks – 463035818_is_not_an_ai Oct 22 '19 at 19:30
https://stackoverflow.com/a/4327317/10809870 – incapaz Oct 22 '19 at 19:31
@NathanOliver sorry for bothering you, how do I find the timeline (unless you give me the link ;) ? – 463035818_is_not_an_ai Oct 22 '19 at 19:32
It's `stackoverflow.com/posts/post_id/timeline` where you can get `post_id` from the URL (it's the number between questions and the question title in the URL). This also works for answers. You just need to click the share button and the post id will be the first number after `a/` in the URL. – NathanOliver Oct 22 '19 at 19:34
@NathanOliver ah ok, thanks again – 463035818_is_not_an_ai Oct 22 '19 at 19:34
No problem. It's a nice tool to have. Do note that SO is no longer maintaining it and it could disappear at any time. – NathanOliver Oct 22 '19 at 19:36
The technical reason is stated in Jerry Coffin's answer in the first duplicate. Lambas aren't recursive so don't have this problem, but then they aren't fully equivalent to nested functions for the same reason. – user207421 Oct 22 '19 at 20:13

Is there a technical reason for not allowing nested function definitions?

0 Answers0