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Re: [wg14/wg21 liaison] P2961R1 syntax for Contracts: viable for C?

From: Aaron Ballman <aaron_at_[hidden]>
Date: Fri, 6 Oct 2023 12:11:15 -0400
On Fri, Oct 6, 2023 at 9:58 AM Timur Doumler <cpp_at_[hidden]> wrote:
> Thanks Aaron,
> > On 6 Oct 2023, at 16:53, Aaron Ballman <aaron_at_[hidden]> wrote:
> > C23 Footnote 186: Standard attributes specified by this document can
> > be parsed but ignored by an implementation without changing the
> > semantics of a correct program; the same is not true for attributes
> > not specified by this document.
> Interesting. It seems a bit ambiguous to me what "parsed but ignored" actually means. If we go with the P2935 (attribute-like) syntax for Contracts and you end up having something like this:
> [[ assert: x != 0 ]];
> Does "parse" mean that you have to actually parse `x != 0` as an expression, since the grammar for contracts says that the thing after the colon is an expression? Or does "when you see `[[`, skip every token until you reach the matching `]]` " also count as "parse"?

It's a footnote, so we're a bit imprecise with the wording of it. But
the intent here is "parse" means "lex and eat tokens until the closing
]], paying attention to balance (, [, and { with ), ], and }". It's
"parsing" because of the balanced tokens and needing to find the
closing ]]. But the goal is for it to be a valid implementation to see
[[, eat balanced tokens until the closing ]], and drop everything on
the floor.


> Cheers,
> Timur

Received on 2023-10-06 16:11:29