Re: [Boost-users] Overcoming AST forward declaration (includes online example)

Subject: Re: [Boost-users] Overcoming AST forward declaration (includes online example)
From: Michael Powell (mwpowellhtx_at_[hidden])
Date: 2018-11-02 21:32:50

On Fri, Nov 2, 2018 at 5:16 PM Michael Powell <mwpowellhtx_at_[hidden]> wrote:
>
> Hello,
>
> Please find the example posted here:
>
> http://wandbox.org/permlink/NI2Luvrw1HF7lF1E

A couple of obvious typos resolved, I think the main culprit(s) now
are the forward declaration concerns:

https://wandbox.org/permlink/tM6vQilplqDOL4v5

> The couple of concerns I have in question at the moment are:
>
> * How to best handle variants throughout the grammar. Can I use
> std::variant? Do I need to use boost::variant? Are there additional
> Spirit features that make this doable?
>
> * Embedded in that question is what to do with "nil" or "empty
> statements" which occurs throughout the grammar at times. I wondered
> if "empty statement" could synthesize "nothing", literally, not
> contribute to a variant alternative, for instance. Other AST examples
> seemed to inject a "struct nil {}" pattern, so I figured maybe this
> was the better approach?
>
> * The real kerfuffle for me at the moment is the AST forward
> declaration. From what I gather in the protocol, this is an absolute
> must have. It most occur before Group, and is also used by Message.
>
> Thoughts? Suggestions?
>
> And, please, before you suggest there are "proto compilers" already
> available: yes, I know, I've been down that road. I am not looking to
> parse the proto itself, per se, but rather do some code generation for
> target language artifacts other than the proto itself.
>
> Toward which end, I am also investigating a protoc compiler plugin
> approach. But I figured, I'd pursue this as a  viable path to solving
> the problem as well, notwithstanding the above challenges.
>
> Thanks in advance!
>
> Cheers,
>
> Michael Powell